Enzyme Kinetics of Acetylcholinesterase

Enzyme Kinetics of Acetylcholinesterase David Romero Perez Enzyme kinetics of Acetylcholinesterase and its behaviour in the presence of Edrophonium. Abstract The aim of the present study was to test the effects of edrophonium on the enzyme kinetics of acetylcholinesterase. The use of s-acetylthiocholine as a substrate with its breakdown by acetylcholinesterase and the later reaction into a coloured product, allowed the utilization of colorimetric technique in conjunction with spectrophotometry. A Michaelis-Menton and a Lineweaver-Burk plot showed edrophonium to be an acetylcholinesterase inhibitor that does not fit with the classical descriptions of competitive, non-competitive or uncompetitive inhibitors. The results though were coherent with previous research that classed edrophonium as a mixed inhibitor at concentrations similar to the ones used in the present study, 10 uM. On the contrary, the same study suggested that edrophonium behaves as a competitive inhibitor at concentrations of 0.1 uM but this concentration was not tested on the present study and, therefore, further research is required. Introduction Chemical reactions are the fundamental basis of all matter and, therefore, of life. The study of the chemistry relevant to life is called biochemistry and inside this discipline the study of enzymes has been of particular importance. Enzymes simply make rare chemical events common enough to allow the accumulation of, otherwise, improvable molecules or products required for life (Laidler, 1997). Thanks to millions of years of evolution the level of sophistication in biological systems has reached high levels, allowing fine-tuned regulation of enzymes and their products (Berg, Tymoczko and Stryer, 2012). Nonetheless, the study of the enzyme kinetics and how their regulation works had to overcome, with great efforts, the technological difficulties of such small and fast reactions (Laidler, 1997). The first studies done on enzyme kinetics were on fermentation. From ancient cultures to the present humans have use fermentation to produce alcohol and bread. But it was not until the 19th century that fermentation started to be studied. Fischer’s lock and key hypothesis was one of the first successful although not completely accurate attempts to explain the process (Laidler, 1997). On 1902 Brown studied invertase, using yeast and sucrose, discovering the Enzyme-Substrate complex (ES) (Kenneth, 2013). This provided the fundamental blocks for the development of the new-born biochemistry discipline. Another hallmark on biochemistry was the work of Leonor Michaelis and Maud Leonora Menten, 1913, Michaelis-Menten equation (E + S →↠ ES →↠ ES ´ → E + products). Their experiment failed but gave us important lessons on the importance of pH on enzyme reactions (Laidler, 1997). The pH is important because most, if not all, enzymes are active only at specific ranges of pH, and usually reach their optimum activity around 7.0 pH. This value is common in biological systems although specialized enzymes may require higher or lower values (Berg, Tymoczko and Stryer, 2012). Also, the previously mentioned researchers produced an easy way of visualizing the data in the form of a graph called the Michaelis-Menten plot. This graph allows quick recognition of important parameters like the maximum activity reached by the enzyme (Vmax) and the amount of substrate required to produce half Vmax (Km) (Berg, Tymoczko and Stryer, 2012; Laidler, 1997). The Michaelis-Menten plot will be used in this study to show both parameters in relation to the enzyme achetylcholinesterase. Acetylcholinesterase is an enzyme of vital importance for the nervous system. As an enzyme is a globular protein mostly released to the inter-synaptic space between neurons’ axons and dendrites. Its purpose there is to break down the neurotransmitter acetylcholine to prevent it from continuously activating acetylcholine receptors on the post-synaptic neuron (Berg, Tymoczko and Stryer, 2012). As with every enzyme other substances can interact with it or with the conformation of the E+S complex. These components are called inhibitors and are usually described as competitive, non-competitive or uncompetitive, although mixed inhibitors have been also described (Berg, Tymoczko and Stryer, 2012; Howard, 2007). For any chemical to be classed as an inhibitor it must have an negative effect on the Vmax and/or Km. The effect on those would decide what type of inhibitor the chemical is. If competitive the inhibitor binds to the catalytic site and Vmax remains the same while Km is increased. On the other side, if non-competitive, it would bind on a different location than the catalytic site, preventing the binding of the substrate. In this case Vmax would be the same but Km would be decreased. In turn, an uncompetitive inhibitor binds to the Enzyme-Substrate complex (ES) and both Vmax and Km, are decreased (Berg, Tymoczko and Stryer, 2012; Howard, 2007). In the present study the kinetics of achetylcholinesterase are tested in the presence or absence of edrophonium in order to investigate if it is indeed an inhibitor and to which class it belongs. These values were found using a combination of spectrophotometry and colourometry techniques. Spectrophotometry is a technique in which light crosses a cuvette containing the solutes. The content of the solution absorbs a certain amount of light depending on the concentration of the coloured chemical, therefore, less light will reach the detector at the other side of the cuvette. This is called the transmittance, and allows us to calculate the absorbance by subtracting the transmittance to 1 (1-T=A). The absorbance increases or decreases with the capacity of the solution to absorb light, giving an accurate reading of changes in solution composition or concentrations as is the case with enzymes in the presence of their specific substrate (Blauch, 2014; Reed, et al., 1998). This is calculated using the Beer-Lambert law which states that absorbance can be obtained by the equation A=Ecl (E=molar absorbitivity, c=concentration, l=longitude of the path of light which is commonly 1cm) (Anon., n.d.) Being the molar absorptivity (E) of 5-thio-2-nitrobenzoic acid 1.3610^4. The Beer-Lam bert equation can be rearranged (Anon., n.d.) to study the concentrations of unknown samples given that A and E are known and it provides the basis to accurate study of enzyme kinetics together with colourometric technique. Colourometry is based in the natural correlation between the amount of coloured chemical in a solution and the intensity of that colour. Therefore, by comparing solutions of known concentration of the same chemical it is possible to determine the concentration of the unknown concentration sample (Lancashire, 2011). To do so, a spectrophotometer is used by setting it up at the specific wavelength that corresponds to the colour of the reaction (Reed, et al., 1998). In some cases the product of the enzymatic reaction may not produce any colour and a modified substrate can be used. As it was explained before, acetylcholinesterase hydrolyses (breaks down) acetylcholine into an acetyl group and choline. The problem when trying to use the colourometric technique to measure the substrate production is that choline is colourless, hence the reason s-acetylthiocholine is used instead. The break down product thiocholine reacts with 5,5’dithiobis acid (DTNB) to produce 5-thio-2-nitrobenzoic acid (E=1.3610^4). This final product is yellow coloured and can be measured using the spectrophotometer at 412nm wavelength, allowing the precise study of acetylcholinesterase kinetics. Materials The agents used in this experiment were phosphate buffer (0.1 M), acetylthiocholine (15mM), DTNB reagent (6mM), acetylcholinesterase enzyme (0.3 u/ml) and water. All of them provided by UCLan School of Biomedical Sciences. In order to create the mixtures Gilson pipettes ( p20, p200 and p1000) with their respective tips were used. In addition, 3ml tubes were used for the initial adding of agents and 1ml standard plastic cuvettes for the spectrometer, which was also used to measure the absorbance. Methods The present study was divided in three parts. The aim of the first part was to find out the effect of enzyme concentration on rate reaction. The second part aimed to find the effect of different substrate concentration on rate reaction. Finally the third part studied the effect of edrophonium on enzyme rate reaction at different substrate concentrations. As a general note, every single dilution was kept at 3.0ml volume, using phosphate buffer as solvent. Also, every single dilution had 0.1ml AChE but in controls it was replaced with 0.1ml phosphate buffer to keep the 3.0ml volume. All mixtures were produce at room temperature. Plastic cuvettes were used to measure up absorbance in a spectrometer at 412 nm wavelength for two minutes, being the result the average per minute of those two minutes. For the first part of the study on effect of enzyme concentration on rate reaction the mixtures were produced as showed in table 1. AGENT VOLUME 1ST MIXTURE VOLUME 2ND MIXTURE VOLUME 3RD MIXTURE STOCK CONC. REACTION CONC. PHOSPHATE BUFFER 1.25 ml 1.2 ml 1.1 ml 0.1 M 50 mM ACETYLTHIOCHOLINE 0.1 ml 0.1 ml 0.1 ml 15mM 0.5 mM DTNB REAGENT 0.1 ml 0.1 ml 0.1 ml 6 mM 0.2 mM AChE 0.05 ml 0.1 ml 0.2 ml 0.3 u/ml 1st-0.005 u/ml 2nd-0.01 u/ml 3rd-0.02 u/ml WATER 1.5 ml 1.5 ml 1.5 ml n/a n/a Table 1 Reaction Mixtures. Before measuring every mixture the spectrometer was blanked with the correspondent control without the enzyme. The second part of the study looked at the effect on rate reaction of different substrate concentrations. The mixtures were produced with the volumes detailed in table 2. ACETYLTHIOCHOLINE (ml) PHOSPHATE BUFFER (ml) DTNB REAGENT (ml) AChE (ml) WATER Reaction conc of Acetylthiocholine (uM) 0.20 1.1 0.1 0.1 1.5 1000 0.10 1.2 0.1 0.1 1.5 500 0.05 1.25 0.1 0.1 1.5 250 0.02 1.28 0.1 0.1 1.5 100 0.01 1.29 0.1 0.1 1.5 50 0.005 1.295 0.1 0.1 1.5 25 Table 2 Composition of mixtures of acetylcholinesterase enzyme reaction without edrophonium. The effect of edrophonium on rate reaction was studied on the third part of the experiment. The mixtures were produced following table 3. Acetylthiocholine (ml) Phosphate Buffer (ml) DTNB Reagent (ml) Edrophonium (ul) AChE (ml) Water (ml) Reaction conc of acetythiocholine (uM) 0.20 1.1 0.1 100 0.1 1.5 1000 0.10 1.20 0.1 100 0.1 1.5 500 0.05 1.25 0.1 100 0.1 1.5 250 0.02 1.28 0.1 100 0.1 1.5 100 0.01 1.29 0.1 100 0.1 1.5 50 0.005 1.295 0.1 100 0.1 1.5 25 Table 3 Composition of mixtures of acetylcholinesterase enzyme reaction with edrophonium. Once the absorbance was recorded, the Beer-Lambert law equation was transformed to calculate the Velocity of 5-thio-2-nitrobenzoic acid (E=1.3610^4) production in Moles/litre/min achieved by every mixture: -A=ECL → C=A/E (L equals 1 per 1 cm of light path length inside the spectrophotometer cuvettes). The full calculations can be consulted in appendix 1. Results For the first part of the study the effect of enzyme concentration on rate reaction was measured and the velocity on nM/L/min was calculated and noted in table 4. Acetylcholinesterase concentration in u/ml Velocity of reaction in ÃŽ ¼M/L/min 0.005 2.05 0.01 3.97 0.02 7.8 Table 4 Calculated Velocity of reaction by acetylcholinesterase concentration. The velocity was plotted against enzyme concentration in graph 1, which shows a linear relationship between both parameters. Graph 1 Enzyme reaction of acetylcholine in response to enzyme concentration. Next the velocities of enzyme reaction at acetylthiocholine concentrations ranging from 25-1000 ÃŽ ¼M in the presence or absence of edrophonium were calculated and noted in table 5. Reaction concentration of Acetylthiocholine (ÃŽ ¼M) Velocity of reaction without edrophonium (ÃŽ ¼M/L/min) Velocity of reaction with edrophonium (ÃŽ ¼M/L/min) 25 2.5 0.15 50 2.87 0.95 100 3.6 1.25 250 3.75 2.57 500 4.34 2.65 1000 6.62 3 Table 5 calculated Velocities of acetylcholinesterase enzymatic reaction with and without edrophonium. Using the data from table 5 a Michaelis-Menton graph was plotted in graph 2 in order to reveal changes in Vmax and Km in the presence or absence of edrophonium. Graph 2 Michaelis-Menton plot of acetylcholine in the presence or absence of edrophonium. Clear differences on Vmax and Km were found between mixtures with or without edrophonium. In its presence Vmax dropped from 4.34 uM/L/ml to 3.01 uM/L/ml. On the contrary, the amount of substrate (s-acetylthiocholine) required to achieve 50% of Vmax was increased from 30 uM/ml to 100 uM/ml. There was a problem with the higher concentration mixture of the absence condition as it produced a higher than expected absorbance. This was examined in the discussion section. A Lineweaver-Burk plot (graph 3) showed the same results with decreased Vmax and increased Km. Graph 3 Lineweaver-Burk plot acetylcholinesterase in the presence and absence of edrophonium. In agreement with what was observed in graph 2, the graph showed that edrophonium is an acetylcholinesterase inhibitor. The kind of inhibitor it belongs to was examined in the discussion section. Discussion When comparing the Michaelis-Menton and the Lineweaver-Burk plots with the standard results of competitive, non-competitive and uncompetitive inhibitors (Berg, Tymoczko and Stryer, 2012), it became clear edrophonium did not belong to any of those. This can be explained by understanding the mode of action of a given inhibitor with the enzyme-substrate complex. Different inhibitors interact with different parts of a given enzyme or at different moments. A competitive inhibitor â€Å"competes† with the substrate for the catalytic site of the enzyme. As a consequence, the Vmax is reduced but if the concentration of the substrate is increased, more substrate would reach the catalytic site, nullifying the effect of the inhibitor although increasing the Km. An uncompetitive inhibitor does not bind to the catalytic site but somewhere else on the enzyme. It binds only once the E+S complex has been formed, decreasing the reaction rate regardless the substrate concentration. As a result the enzyme can not reach its normal Vmax and the Km is decreased. On the other hand, a noncompetitive inhibitor does not need the E+S complex to bind to the enzyme and does not decrease E+S formation. However, the E+S+I complex would not create a product, inactivating the enzyme. Basically, the noncompetitive inhibitor has taken a percentage of the active enzy me from the population, decreasing the Vmax but maintaining the same Km for the rest of the active enzyme population (Berg, Tymoczko and Stryer, 2012). The results of the present study suggest that edrophonium decreases the Vmax whilst increasing the Km and this effect can not be overcome by increasing substrate concentration. As a result, it can be classed as a mixed inhibitor, which inhibits the binding of the enzyme to the substrate and, at the same time, inactivates a proportion of the enzyme population (Berg, Tymoczko and Stryer, 2012). This has been supported by previous research (Robaire Kato, 1975) that found edrophonium to be a competitive inhibitor at concentrations of 0.1 uM but a mixed inhibitor at concentrations like the used in the present study, 10 uM. There were some limitations with the materials used. Plastic cuvettes were used instead of glass ones which are more suitable for organic solvents (Reed, et al., 1998). Also, the relative pipetting inexperience of the researches might have affected the accuracy of the resulting mixtures, hence the odd results for the mixture of higher substrate concentration on the absence condition. In future research it is recommended to improve pipetting accuracy maybe by using an automated pipetting system. Also, the timing in enzymatic reactions is critical, as these reactions occur often in seconds or even milliseconds (Laidler, 1997). Therefore, a multiplate spectrophotometer reader could be used to measure the absorbance of the mixtures. This would avoid any potential differences and delays from the moment the mixture is done to its reading. Also, lower concentrations of edrophonium (0.1 uM) should be tested to corroborate Robaire and kato’s (1975) research. In conclusion, in agreement with previous research (Bonaire Kato, 1975), the data points at edrophonium as an acetylcholinesterase mixed inhibitor at least at high concentrations (10 uM). Nonetheless, it needs to be confirmed in future research that edrophonium is also a competitive inhibitor at low concentration. At the same time, the technique could be optimized by the use of automated means in order to improve accuracy given the odd results produced by poor pipetting accuracy. References Anon (n.d.) Beers Law. Available: http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/beers1.htm. Last accessed 15th Jan 2014. Berg, J. M., Tymoczko, J. L. and Stryer, L. (2012) Biochemistry, 7th ed. New York: Freeman. Blauch D. N. (2014) Spectrophotomery. Available: http://www.chm.davidson.edu/vce/spectrophotometry/Spectrophotometry.html. Last accessed 15th Jan 2014. Howard, A. J. (2007) Enzyme inhibition and regulation, CSRRi,iit, [online]. Available at: http://csrri.iit.edu/~howard/biochem/lectures/enzymeinhibition.html. Last accessed 15th Jan 2014. Kenneth, A. J. (2013) A century of enzyme kinetic analysis, 1913 to 2013. FEBSLetters. 587, 2753-2766. Laidler, K. J. (1997) A brief history of enzyme kinetics. In: A. Cornish-Bowden ed. New Beer in an Old Bottle: Eduard Buchner and the Growth of Biochemical Knowledge. Valencia: Universitat de Valencia, pp. 127-133. Lancashire, R. J. (2011) EXPERIMENT 36 COLOURIMETRIC DETERMINATION OF PHOSPHATE. Available: http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt36.html. Last accessed 15th Jan 2014. Reed, R. Holmes, D. Weyers, J. Jones, A. (1998) Practical Skills in Biomolecular Sciences. 4th ed. Essex: Pearson. 310-313. Robaire, B., Kato, G. (1975) Effects of Edrophonium, Eserine, Decamethonium, d-Tubocurarine, and Gallamine on the Kinetics of Membrane-Bound and Solubilized Eel Acetylcholinesterase. MOLECULAR PHARMACOLOGY. 11 (6), 722-734. Appendix 1 Velocity calculations Normal absorbances (nM) Divided by E Velociy (ÃŽ ¼M/L/min) 1/Velocity 0.034 2.5 0.4 0.039 2.87 0.35 0.049 1.3610^4 3.6 0.277 0.051 3.75 0.266 0.059 4.34 0.23 0.090 6.62 0.15 absorbances in the presence of edrophonium (nM) Divided by E Velociy (ÃŽ ¼M/L/min) 1/Velocity 0.002 0.15 6.6 0.013 0.95 1.05 0.017 1.3610^4 1.25 0.8 0.035 2.57 0.39 0.036 2.65 0.37 0.041 3 0.33

Sexuality at Different Life Stages

Sexuality at Different Life Stages Sexuality at Different Life Stages Through the different stages of our lives we experience sexuality in one way or another. In the stage of infancy we experience sexuality by the suckling our fingers to vaginal lubrication or erections. As we grow into older children we experience sexuality in the form of kissing and games such as doctor, or I will show you mine if you show me yours. In the case of Ana she is in the stage of adolescence. This is the stage when our body starts going through puberty and our sexual hormones are raging.This is also the time when we want the adults to be the most informative and answer questions that we may have without judgment. Ana is at the point in her life where she is at a fork in the road and is unsure of what she wants to do, and is feeling like she is being torn because of comments she is hearing from her mom. As much as her mom thinks that she is trying to keep her daughter. The next stage in life is adulthood. During adulthood there can be many different ways that one will experience sexuality.In the case of Tom and Susan they are both retired and although Susan is newly retired and has found interest in sex again Tom is not showing any interest. This could be a simple issue that could be taken care of with talking or even with medication. Then you can have the issue like in the case of Bill and being paralyzed which one may need to be informed of the possibilities into how he can be intimate with his partner. It is stated in Ana’s case that she is in the adolescent stage of her life and in love with her boyfriend who she has been dating for three years now.Her boyfriend is three years older and has putting pressure on her to have sex, and her mom is telling her that Ana’s boyfriend is going to take advantage of her because she is young. Ana needs to understand that what was right for her mother, or for her boyfriend may not be right for her. Ana needs to get away from the people that are in her ears and she needs to listen to what is in her heart. I do not believe in telling you Ana that I condone sex among adolescence, because I do not.Although I feel that the more informed you are about not only the possibilities that could happen from having sex, such as teen pregnancy and STD’s, the more you as an individual will be able to make an informed decision. When deciding to have sex with someone you need to stop and think about the reason you are having sex with this person. Is it because you want to or is it because you are feeling pressure from that person to have sex? You need to know what you morally believe in and be able to stand up for what you believe in.As far as your mother you need to let her know and to put her mind at ease that when you are ready to have sex with someone that you will make sure that you are having sex for all the right reasons and that you will be responsible about the decision you make. Keeping the line of communica tion open between you and your parents will help in being able to be informed about sex and the emotions that go along with it. A man can have sex with someone and not have it mean anything, but unfortunately for girls it is not the same.When a woman has sex with someone it is because she has strong feelings for that person and want to be together with that person and because she loves that person, and unfortunately that is not always the case for the person you decide to have a sexual relationship with. Tom and Susan you have both entered a stage in your life where you are at different stages sexually. Susan you are feeling sexual desire again in your stage of life whereas Tom may be at the stage where he is unsure that he may be able to perform.We all as individuals go through this in this stage of life because life takes a toll on us from our appearance being changed and looking older to maybe sexually things not working the way we want them to and this can play a big role in how we feel about ourselves mentally. As far as the way you look, all that matters is what your partner thinks of you and Tom thinks that your are more beautiful than the day he married you. As for you Tom being nervous about the possibility of things not working when you want them to can create a lot of unnecessary stress that could add to the problem of things not working.We can try one of two things, you can go home leave all your worries in my office and just enjoy each other and remind each other what you guys mean to one another, or we can look into prescribing something that will help you when you find yourselves wanting to be in that intimate moment. In the case of Bill he is at a point in his life that most adults if they are lucky will never have to go through and that is being able to be intimate with someone when you are paralyzed from the waist down. With a situation like this you as the individual going through the problem needs to know and understand the extent of your i njury.Knowing the extent of the injury would be able to let you know if you were able to achieve an erection or not. With everything that goes on between couples normally this is one more thing that can and will cause stress. There are many ways that you and your mate can find pleasure from each other you just need to be willing to think outside of the box. We as individuals go through so much as we grow and mature, that we often complicate the simple things in life instead of taking things in stride. In the cases that we went through we discussed many different ideas that can either be complicating a relationship, or making it better.

National Culture of Malaysia Essay

Professor Geert Hofstede conducted one of the most comprehensive studies of how values in workplace are influenced by culture. He defines these dimensions as follows: Power Distance: ‘the extent to which the less powerful members of organizations and institutions (like the family) expect and accept that power is distributed unequally’. Uncertainty Avoidance: ‘intolerance for uncertainty and ambiguity’. Individualism versus Collectivism: ‘the extent to which individuals are integrated into groups’. Masculinity versus Femininity: ‘assertiveness and competitiveness versus modesty and caring’. Figure 1 Figure 1 shows the statistic of national culture in Malaysia through the lens of the 5-D Models. From the graph, we can get a deep overview of Malaysia culture relative to other world culture. 1) Power Distance: Malaysia has a high power distance because of the hierarchy system among people. The hierarchy is referred to the rank (Tan Sri, Datuk, Puan Sri), the level of knowledge (Professor, Doctor) or the seniority (grandpa, grandma, brother, sister). The value of the high power distance is respect and humble. It is ethically when employee give respect to their manager. 2) Individualism: Malaysia is categorized as collectivism because Malaysia emphasizes the good of the group, community, or society over and above individual gain. Three difference races (Chinese, Indian and Malay) are working together to develop the economy of Malaysia and increasing the quality of life. The value of collectivism is support and unity to gain equal advantages. It is non-ethical if these difference races do not respect each other and have racial bias. 3) Masculinity: Masculine cultures are described as being dominated by money and power relationships and often are results-oriented while feminine cultures are more connected with interpersonal relationship and process-oriented. From figure 1, Malaysia possesses masculinity and femininity culture. The masculinity culture in organization is characterized as command structure and expects employees to obey the instructions without questions. Meanwhile, femininity culture more focused on sharing emotions, democratic, cooperation and communication. 4) Uncertainty avoidance: Uncertainty avoidance is about the way approached by society to avoid unknown situation in the future. Malaysia is categorize as low uncertainty avoidance because individuals are less concerned by the ambiguity and uncertainty and have a greater tolerance for a variety of option. Such society are less ruleoriented, take more risks and more ready to accept change. In multinational corporation environment, the need for the product development processes and organizational routines are increases to generate competitive advantage in multiple nations. Low uncertainty avoidance can create the value of critical thinking among employee to solve the problem and cultivate the sense of responsibility for the decision making. It is an ethical situation for being prepared for the uncertainty and generate creative and innovative person in the country. Malaysia nowadays can be categorized as masculinity culture. People are live in order to work. Money and power is the sign of success driven by the competition and achievement. The value of the masculinity is the competiveness between workers to become the best and gain profit. It is ethical when we are trying our best to obtain great income or improve our quality of life.

Find out Why a Goldfish Turns White If Left in the Dark

The short answer to this question is probably not white, though the color will become much paler. Goldfish Can Change Colors Goldfish and many other animals change color in response to light levels. Pigment production in response to light is something were all familiar with  since this is the basis for a suntan. Fish have cells called chromatophores that produce the pigments that give coloration or reflect light. The color of a fish is determined in part by which pigments are in the cells (there are several colors), how many pigment molecules there are, and whether the pigment is clustered inside the cell or is distributed throughout the cytoplasm. Why Do They Change Color? If your goldfish is kept in the dark at night, you may notice it appears a little paler when you turn on the lights in the morning. Goldfish kept indoors without full-spectrum lighting are also less-brightly colored than fish exposed to natural sunlight or artificial lighting that includes ultraviolet light (UVA and UVB). If you keep your fish in the dark all the time, the chromatophores wont produce more pigment, so the fishs color will start to fade as the chromatophores that already have color naturally die, while the new cells arent stimulated to produce pigment. However, your goldfish wont become white if you keep it in the dark because fish also get some of their coloration from the foods they eat. Shrimp, spirulina, and fish meal naturally contain pigments called carotenoids. Also, many fish foods contain canthaxanthin, a pigment added for the purpose of enhancing fish color.