1. Enzymes are biological molecules thatcatalyze(i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products.www.agscientific.com/molecular-biology/molecular-biology.htmlEnzymesEnzymesare biological molecules that catalyze (i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates sufficient for life.Their functionality depends on how proteins are folded, what they bind to, and what they react with. For protein-based catalysts, amino acid polarization lies at the core of catalytic activity.Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.Catalaseis a commonenzymefound in nearly all living organisms that are exposed to oxygen, where it functions tocatalyzethe decomposition ofhydrogen peroxidetowaterandoxygen.[1]Catalase has one of the highestturnover numbersof all enzymes; one molecule of catalase can convert 40 million molecules of hydrogen peroxide to water and oxygen each second.[2]Catalase is atetramerof four polypeptide chains, each over 500amino acidslong.[3]It contains fourporphyrinheme(iron) groups that allow the enzyme to react with the hydrogen peroxide. The optimumpHfor human catalase is approximately 7,[4]and has a fairly broad maximum (the rate of reaction does not change appreciably at pHs between 6.8 and 7.5).[5]The pH optimum for other catalases varies between 4 and 11 depending on the species.[6]The optimum temperature also varies by species.[7]https://www.princeton.edu/~achaney/tmve/wiki100k/docs/Catalase.html

Action[edit]The reaction of catalase in the decomposition of hydrogen peroxide in living tissue:2 H2O2 2 H2O + O2The presence of catalase in a microbial or tissue sample can be tested by adding a volume ofhydrogen peroxideand observing the reaction. The formation of bubbles,oxygen, indicates a positive result. This easyassay, which can be seen with the naked eye, without the aid of instruments, is possible because catalase has a very highspecific activity, which produces a detectable response.Molecular mechanism[edit]While the complete mechanism of catalase is not currently known,[14]thereactionis believed to occur in two stages:H2O2+ Fe(III)-E H2O + O=Fe(IV)-E(.+)H2O2+ O=Fe(IV)-E(.+) H2O + Fe(III)-E + O2[14]Here Fe()-E represents theironcenter of thehemegroup attached to the enzyme. Fe(IV)-E(.+) is a mesomeric form of Fe(V)-E, meaning the iron is not completely oxidized to +V, but receives some "supporting electrons" from the heme ligand. This heme has to be drawn then as a radical cation (.+).As hydrogen peroxide enters theactive site, it interacts with theamino acidsAsn147 (asparagineat position 147) andHis74, causing aproton(hydrogenion) to transfer between the oxygen atoms. The free oxygen atom coordinates, freeing the newly formed water molecule and Fe(IV)=O. Fe(IV)=O reacts with a second hydrogen peroxide molecule to reform Fe(III)-E and produce water and oxygen.[14]The reactivity of the iron center may be improved by the presence of the phenolateligandofTyr357in the fifth ironligand, which can assist in theoxidationof the Fe(III) to Fe(IV). The efficiency of the reaction may also be improved by the interactions of His74 and Asn147 withreaction intermediates.[14]In general, the rate of the reaction can be determined by theMichaelis-Menten equation.[15]Catalase can also catalyze the oxidation, byhydrogen peroxide, of various metabolites and toxins, includingformaldehyde,formic acid,phenols,acetaldehydeandalcohols. It does so according to the following reaction:H2O2+ H2R 2H2O + RThe exact mechanism of this reaction is not known.Any heavy metal ion (such as copper cations incopper(II) sulfate) can act as anoncompetitive inhibitorof catalase. Furthermore, the poisoncyanideis acompetitive inhibitorof catalase at high concentrations ofhydrogen peroxide.[16]Three-dimensionalprotein structuresof the peroxidated catalase intermediates are available at theProtein Data Bank. This enzyme is commonly used in laboratories as a tool for learning the effect of enzymes upon reaction rates.Cellular role[edit]Hydrogen peroxide is a harmful byproduct of many normalmetabolicprocesses; to prevent damage to cells and tissues, it must be quickly converted into other, less dangerous substances. To this end, catalase is frequently used by cells to rapidly catalyze thedecompositionof hydrogen peroxide into less-reactivegaseousoxygenand water molecules.[17]The true biological significance of catalase is not always straightforward to assess: Mice genetically engineered to lack catalase are phenotypically normal, indicating this enzyme is dispensable in animals under some conditions.[18]A catalase deficiency may increase the likelihood of developingtype 2 diabetes.[19][20]Some humans have very low levels of catalase (acatalasia), yet show few ill effects. The predominant scavengers of H2O2in normal mammalian cells are likelyperoxiredoxinsrather than catalase.[citation needed]Human catalase works at an optimum temperature of 45C,.[6]In contrast, catalase isolated from thehyperthermophilearchaeonPyrobaculum calidifontishas a temperature optimum of 90C.[21]Catalase is usually located in a cellular, bipolar environmentorganellecalled theperoxisome.[22]Peroxisomes in plant cells are involved inphotorespiration(the use of oxygen and production of carbon dioxide) and symbioticnitrogen fixation(the breaking apart ofdiatomicnitrogen(N2) to reactive nitrogen atoms). Hydrogen peroxide is used as a potent antimicrobial agent when cells are infected with a pathogen. Catalase-positive pathogens, such asMycobacterium tuberculosis,Legionella pneumophila, andCampylobacter jejuni, make catalase to deactivate the peroxide radicals, thus allowing them to survive unharmed within thehost.[23]Catalase contributes to ethanol metabolism in the body after ingestion of alcohol, but it only breaks down a small fraction of the alcohol in the body.[24]http://en.wikipedia.org/wiki/Catalase#Action

enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium. enzyme activity depend on the temperature, ionic conditions, and pH of the surroundings.http://www.csun.edu/~aef21890/coursework/695/science_kit/enzyme-catalase.htmApplications to everyday life:This reaction is important to cells because hydrogen peroxide (H2O2) is produced as a byproduct of many normal cellular reactions. If the cells did not break down the hydrogen peroxide, they would be poisoned and die.enzymesare proteins that catalyze biochemical reactions without altering the reaction equilibrium and theactivities of enzymes depend onthe temperature, ionic conditions, and the pH of the surroundings.catalaseBIOCHEMISTRY1. an enzyme that catalyses the reduction of hydrogen peroxide.

1. Catalaseis a common enzyme found in nearly allliving organismsthat are exposed to oxygen, where itfunctionsto catalyze the decomposition of hydrogen peroxide to water and oxygen.

Catalase (EC 1.11.1.6) is an enzyme which is present mainly in the peroxisomes of mammalian cells. It is a tetrameric enzyme consisting of four identical, tetrahedrally arranged subunits of 60 kDa, each containing in its active center a heme group and NADPH. Catalase has two enzymatic activities depending on the concentration of H2O2. If the concentration of H2O2 is high, catalase acts catalytically, i.e. removes H2O2 by forming H2O and O2 (catalatic reaction). However, at a low concentration of H2O2 and in the presence of a suitable hydrogen donor, e.g. ethanol, methanol, phenol, and others, catalase acts peroxidically, removing H2O2, but oxidizing its substrate (peroxidatic reaction). The review article presents current knowledge about the structure, properties, and functions of catalase in living organisms.

http://www.ncbi.nlm.nih.gov/pubmed/16618987

Catalase is a common antioxidant enzyme which is produced naturally in almost all living organisms. The reactions in catalyses are important to life, for example, it helps the body to break down hydrogen peroxide (a powerful and harmful oxidizing agent) into oxygen and water, thus it prevents the accumulation of carbon dioxide bubbles in the blood. Catalase is a very potent enzyme; one molecule of catalase can decompose millions of hydrogen peroxide molecules into oxygen and water. It also uses hydrogen peroxide to oxidize potentially harmful toxins in the body including formaldehyde, formic acid, alcohol, and phenol.

Read more :http://www.ehow.com/about_5521462_role-catalase.html

Cellular function Oxygen is crucial to life; however, when we use oxygen our bodies constantly produce free radicals. Free radicals are chemically unstable molecules or atoms. They also make other molecules or atoms in the body very unstable, thus damaging proteins, cell membranes, and even DNA structure. This is a process which can lead to permanent damage to cells and tissues resulting in infection, mental decline, depressed immunity system, joint disease, and heart disease. Free radicals are also considered to play an important role in the aging process.Catalase is constantly in battle against the effect of free radicals to the body. It transforms harmful superoxide radicals into hydrogen peroxide which later breaks down into water and oxygen.

http://www.reviewmylife.co.uk/blog/2008/06/05/the-effect-of-substrate-concentration-on-the-activity-of-the-enzyme-catalase/Enzymes such as Catalase are protein molecules which are found in living cells. They are used to speed up specific reactions in the cells. They are all very specific as each enzyme just performs one particular reaction.Catalase is an enzyme found in food such as potato and liver. It is used for removing Hydrogen Peroxide from the cells. Hydrogen Peroxide is the poisonous by-product of metabolism. Catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen as shown in the equations below.Formula: Catalase Hydrogen Peroxide---------------------->Water + Oxygen Catalase 2H2O2------------------->2H2O+O2It is able to speed up the decomposition of Hydrogen Peroxide because the shape of it's active site matches the shape of the Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction.Probable PrecautionsTo ensure this is a fair test all the variables except for the concentration of Hydrogen Peroxide must be kept the same for all the experiments. Variables that must not be altered include:-Temperature, yeast concentration, type of yeast, batch of yeast, volume of yeast, volume of hydrogen peroxide, air pressure and humidity.When measuring the volumes of Hydrogen Peroxide, Yeast and Water the measurement should be taken by looking at the scale at an angle of 90 degrees to it to avoid any parallax error.

INFOWhen the concentration of Hydrogen Peroxide is increased, the rate of reaction increases at a directly proportional rate until the concentration of Hydrogen Peroxide reaches about 16%. If you double the concentration of Hydrogen Peroxide then the rate of reaction doubles as well. When the concentration is doubled from 8-16% the rate goes up from 1.65-2.97 Cm3 Oxygen produced per second, which is an increase of 1.8 times. I would expect the rate to increase two times if the Hydrogen Peroxide concentration is increased two times because there are twice as many substrate molecules which can join onto the enzymes active sites. The reason that the number is less than two times could be put down to the fact that at 16% the Enzyme's active sites may already be close to being saturated with Hydrogen Peroxide. There may also be some experimental error which causes the inaccuracies.After 16% the increase in the rate of reaction slows down. This is shown by the gradient of the graph going down. At this point virtually all the active sites are occupied so the active sites are said to be saturated with Hydrogen Peroxide. Increasing the Hydrogen Peroxide Concentration after the point of saturation has been reached will not cause the rate of reaction to go up any more. All the active sites are being used so any extra Hydrogen Peroxide molecules will have to wait until an active site becomes available.The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all the active sites are being used all the time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction.The diagram below shows what happens.[not reproduced]Limitations

To help make this experiment more accurate, I repeated it three times and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables except for the concentration of Hydrogen Peroxide the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example:a) There is a slight delay between pouring the Hydrogen Peroxide into the yeast, putting the bung on and starting the stopwatch. This will slightly affect all the results but as I carried out all the three steps in the same way for all the experiments it should not make any difference to the overall result.b) It is also impossible to precisely measure out the amounts of Hydrogen Peroxide, Yeast and Water each time. As the scale on the pipettes shows the volume to the nearest mm3 the volume of the solutions that I used should be correct to the nearest mm3. The volume of gas in the test tube to start with is slightly affected by the amount which the bung is pushed down each time, if the bung is pushed down further then the volume in the tube will be less so the 30cm3 of gas is reached faster.c) Due to the fairly slow speed of our reactions it is only possible to measure the time of the reaction to the nearest 0.1 second even though the stopwatch shows the measurements to the nearest 0.01 second.