Catalase on Hydrogen Peroxide

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Abstract
The aim of this study was to test the rate of reactivity of the enzyme catalase on hydrogen peroxide while subject to different concentrations of an inhibitor. The hypothesis was that hydrogen peroxide will be broken down by catalase into hydrogen and oxygen, where a higher concentration of inhibitor will yield less oxygen, resultant of a lower rate of reaction. Crushed potato samples of equal weight were placed in hydrogen peroxide solutions of various temperatures. The results showed that less gas was produced as the concentration of the inhibitor rose. This Is because more enzymes were inhibited, and so less active sites were available for reaction. Reasearch and rationale

Hypothesis:
Catalase will break down hydrogen peroxide in water and hydrogen. A higher concentration of inhibitor will yield a slower rate of reaction, thus yielding less oxygen in a given time. Null hypothesis:

Catalase will break down hydrogen peroxide in water and hydrogen. The concentration of the inhibitor will have no effect on the rate of this reaction.
Supporting knowledge:
Enzymes function as biological catalysts, increasing the rate of reactions that take place within organisms. Catalase is an enzyme found in the vast majority of organisms that are exposed to oxygen, making it very common. It catalyses the decomposition of hydrogen peroxide into water and oxygen. Hydrogen peroxide is a molecule that can attack sulphur atoms and metal ions in protein molecules, and with the aid of iron ions is potentionally mutagenic. Catalase is an extremely effective enzyme, and can break down millions of hydrogen peroxide molecules in a single second. As such, it can be seen how important and effective catalase is to oxygen-exposed organisms. As with the majority of enzymes, it has an optimum pH of approximately 7, though the optimum can vary by species. Haliotis discus discus, a type of shellfish, for example, has catalase which works at an optimum pH of 10.5.

There are a number of factors which affect the rate of reaction of catalase. As stated, pH is one. Concentration of both catalase and hydrogen peroxide, concentration of co-enzymes (Fe3+ in human catalase) and temperature are all variables that affect the rate of reaction. These can all be regarded as limiting factors, as they can only affect the rate of reaction to a certain point when alone. That is to say, the reaction will not work as best it can if all factors are not at an optimum standard.

The poison cyanide acts as a competitive inhibitor, it strongly binds to the haem of catalase, stopping an enzyme-substrate complex from forming. Heavy metal ions, such as copper ions in copper (II) sulphate, act as non-competitive inhibitors on catalase. Competitive inhibitors act by binding to the actual active site of the enzyme, thus stopping an enzyme substrate complex from forming. Competitive inhibition, this can be reversed by increasing the concentration of the substrate. Non-competitive inhibitors bind to a site other than the active site, known as the allosteric site. As such, it is able to bind even to an enzyme-substrate complex. These inhibitors are usually reversible, but are not affected by concentration of the substrate in the way that competitive inhibitors are. Copper acts as a non-competitive inhibitor of catalase. Copper, as a heavy metal, reacts strongly with sulphydryl groups in proteins. This can cause the protein to precipitate, and thus change the shape of the active site. This type of inhibition is irreversible, as the protein becomes covalently modified., Inhibition affects the rate of enzymatic reactions differently than extremes of pH and temperature, which both affect the protein in a non-specific way. These factors reduce the rate of reaction by a process called irreversible enzyme inactivation. This is where the whole protein structure is destroyed, or denatured. Non-competitive inhibitors work by specifically altering the structure of the enzymes...
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