Enzymes Enzymes are biocatalysts the catalysts of life. A catalyst is defined as a substance that increases the velocity or rate of a chemical reaction without itself undergoing any change in the overall process. Enzymes may be defined as biocatalysts synthesized by living cells. Their basic properties include, They are protein in nature (exception - RNA acting as ribozyme), colloidal and thermolabile in character, and specific in their action. In the laboratory, hydrolysis of proteins by a strong acid at 100oC takes at least a couple of days. The same protein is fully digested by the enzymes in gastrointestinal tract at body temperature (37oC) within a couple of hours. This remarkable difference in the chemical reactions taking place in the living system is exclusively due to enzymes. The very existence of life is unimaginable without the presence of enzymes. Enzymes catalyse a specific substance called a substrate. Role of enzymes in biochemical reactions Enzymes are biological catalysts that increase the rate or velocity, v, of many physiologic reactions yet are not used up in the reaction and are synthesized by living cells. Enzymes are specialized proteins found and produced by living cells and act as biological catalysts a. In the absence of enzymes, most reactions in the body would proceed so slowly that life would be impossible. Some chemical reactions are only possible by enzymes. C. A deficiency in enzyme activity can cause disease. a. Inherited absence or mutations in enzymes involved in critical metabolic pathways e.g. the urea cycle or glycogen metabolism are referred to as inborn errors of metabolism. If not detected soon after birth, these conditions can lead to serious metabolic derangements in infants and even death. b. An enzyme deficiency can produce a deficiency of the product of the reaction it catalyzes, which may inhibit other reactions that depend on availability of that product. c. Accumulation of the substrate or metabolic byproducts of the substrate due to an enzyme deficiency can have profound physiologic consequences. d. Most inborn errors of metabolism manifest after birth because the exchange of metabolites between mother and fetus provides for fetal metabolic needs in utero. e. Therapeutic strategies for enzyme deficiency diseases include dietary modification and potential gene therapy or direct enzyme replacement

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