Enzymes

Enzymes are specialized proteins that function in the acceleration of chemical reactions. Many reactions required for the normal activity of cells would not proceed fast enough at the pH and temperature of the body without these specialized proteins. An apoenzyme is the protein part of an enzyme and it is catalytically inactive. Cofactors are small organic or inorganic molecules that an apoenzyme requires for its activity. The specificity of an enzyme is determined by the structure of its substrate-binding site, known as the active site of the enzyme. Some enzymes will only react with one substrate, whereas others will react with a range of substrates. This paper will look at some of the properties of enzymes and how they work.

Quantitation of enzymes: Enzymes can increase the rate of a reaction by a factor of 109 to 1012 times the rate of the uncatalyzed reaction. Most of this rate enhancement can be accounted for by four processes: acid-base catalysis, substrate strain (transition state stabilization), covalent catalysis, and entropy effects. The activity of an enzyme is determined by measuring the disappearance of the reactants or the appearance of the products of the reaction, and is expressed as moles of product formed per minute. The velocity of the reaction is expressed in terms of change in the concentration of substrate or product per unit time. The rate refers to the change in total quantity (moles or grams) per unit time. These terms, v

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xamples of sequential mechanisms are found among the dehydrogenases in which the second substrate is a coenzyme (e.g. NAD+, FAD, etc.). The release of product may or may not be ordered in either mechanism. Ping pong mechanism: In the ping pong mechanism, the enzyme combines with substrate A and a product is released. The altered enzyme then binds substrate B, and a second product is released. An example of this is the reaction of transaminase. The enzyme-bound pyridoxal phosphate (vitamin B, coenzyme) accepts the alpha-amino group from the first amino acid, which is then released from the enzyme as an alpha-keto acid. The acceptor alpha-keto acid is then bound to the enzyme, and the bound amino group is transferred to it, forming a new amino acid, which is then released from the enzyme. Inhibitors of enzymes Reversible inhibitors: Much of current drug therapy is based on inhibition of specific enzymes by a substrate analog (1:147). Drugs are designed to inhibit a specific enzyme in a metabolic pathway. This application is most readily appreciated with antiviral (e.g. AZT), antibacterial (e.g. sulfanilamide), and antitumor drugs (e.g. methotrexate) that are administered to patients under conditions of limited toxicity. Su

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