2H2O2 + Catalase → 2H2O + O2 + Catalase
What is Catalase?
Enzymes are very large and complex organic molecules that are synthesized by the cell to perform very specific functions. These biological catalysts are important because they speed up the rate of the reaction they catalyze that would otherwise be too slow to support life. Catalase is an enzyme present in the cells of plants, animals and aerobic (oxygen requiring) bacteria. It promotes the conversion of hydrogen peroxide, a powerful and potentially harmful oxidizing agent, to water and molecular oxygen.
2H2O2 to 2H2O + O2
Catalase also uses hydrogen peroxide to oxidize toxins including phenols, formic acid, formaldehyde and alcohols.
H2O2 + RH2 to 2H2O + R
Where is it found and what does it do?
Catalase is located in a cell organelle called the peroxisome. Peroxisomes in animal cells are involved in the oxidation of fatty acids, and the synthesis of cholesterol and bile acids. Hydrogen peroxide is a byproduct of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. In both cases catalase prevents the hydrogen peroxide from harming the cell itself. Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule N2 to reactive nitrogen atoms). Hydrogen peroxide is produced as an intermediate during these chemical processes and must be removed to prevent damage to cellular machinery. Aerobic (oxygen requiring) bacteria produce hydrogen peroxide as a byproduct of metabolism. This fact is used when identifying bacteria. If hydrogen peroxide is added to a bacterial colony and bubbles are produced, this is evidence of oxygen production and confirms that the colony is aerobic.
Prokaryotes, organisms like bacteria that lack a nuclear membrane, also lack membrane bound organelles such as peroxisomes. Antioxidant enzymes like catalase and superoxide dismutase are located in the periplasmic space which is the space between the inner and outer membranes of the cell wall. There are numerous enzymes located here that would be toxic if they were found inside the cell. The catalase found here can act on toxic molecules that are transported to the periplasm or the enzyme can be released outside the bacterial wall where it can act on toxic molecules in the environment. Catalase that is released by the bacteria plays a role in protecting the bacteria from being destroyed by white blood cells during an infection.
What does Catalase look like?
Each molecule of catalase is a tetramer of four polypeptide chains. Each chain is composed of more than 500 amino acids. Located within this tetramer are four porphyrin heme groups that are very much like the familiar hemoglobins, cytochromes, chlorophylls and nitrogen-fixing enzymes in legumes. The heme group is responsible for catalase’s enzymatic activity. Catalase has one of the highest turnover rates for all enzymes: one molecule of catalase can convert 6 million molecules of hydrogen peroxide to water and oxygen each minute.
What factors affect the activity of Catalase
pH: pH is a measure of the acidity or hydrogen ion concentration of a solution. It is measured on a scale of 0-14 with pH values below 7 being acidic, values above 7 being basic and a value around 7 is neutral. As the pH drops into the acidic range an enzyme tends to gain hydrogen ions from the solution. As the pH moves into the basic range the enzyme tends to lose hydrogen ions to the solution. In both cases the changes produced in the chemical bonds of the enzyme molecule result in a change in conformation that decreases enzyme activity.
C A T A L A S E
.....Catalase is nearly ubiquitous among organisms that can grow in the presence of oxygen (air). ..The major function of catalase within cells is to prevent the accumulation of toxic levels of hydrogen peroxide formed as a by-product of metabolic processes - primarily that of the electron transport pathway. ..The only exceptions are the "lactic acid bacteria," which cannot synthesize the fundamental building block porphyrin, and hence do not even possess cytochromes that would otherwise make the toxic H2O2.
.....Each molecule of catalase has four polypeptide chains, each composed of more than 500 amino acids, and nested within this tetrad are four porphyrin heme groups - very much like the familiar hemoglobins, cytochromes, chlorphylls and nitrogen-fixing enzymes in legumes. ..(Catalase may also take part in some of the many oxidatic reactions that occur in all cells.)
.....In the absence of catalase, this reaction occurs spontaneously, but VERY slowly. ..Catalase speeds up the reaction rate many thousands of fold. In today's experiment, a rate for this reaction will be determined.
.....Much can be learned about enzymes by studying the kinetics (particularly the changes in rate) of enzyme-catalyzed reactions. ..For example, it is possible to measure the amount of product formed, or the amount of substrate used, from the moment the reactants are brought together until the raction has stopped.
ENZYMES
affects the three-dimensional structure of all enzymes. Enzymes are made up of amino acids.
Each amino acid has a -NH2 group and a -COOH group, not to mention certain amino acids that have an extra -COOH group (e.g. aspartate) or an extra -NH3+group (e.g. asparagine). pH is all about concentration of H+ ions. At low pH and high H+ concentration the predominant forms of these groups will be -COOH and -NH3+ or the "protonated forms". At neutral pH the predominant forms will be -COO and -NH3+. At high pH the predominant forms will be -COO- and -NH2. However the actual pH at which each group becomes ionised depends on the particular amino acid and also the environment in which the enzyme is found. The usual way of expressing this is the pK value: this pK is the pH at which half of the groups are ionised.
Interactions between these positive and negative charges are a very important part of what holds the structure together in an enzyme. These links are known as salt links, salt bridges or electrostatic interactions and involve a + to - attraction. Changing the pH therefore alters the properties of these salt bridges. Even a small shift away from optimum pH might mean one of these salt bridges is affected and therefore the shape and activity and stability of the protein will also be affected.