Medical brain notes 25

  Introduction   For all enzymatic processes the rate of the reaction depends upon the concentration of the enzyme and its substrates, other conditions like temperature and pH being constant. Figure 9.1 shows the relationship between the substrate and product concentrations. Although the velocity increases linearly with enzyme concentration, at constant enzyme concentration it increases hyperbolically as the substrate concentration increases. This indicates that the enzyme has a definite number of sites to combine with substrate. When all sites are occupied, no further rate enhancement occurs and the enzyme is saturated with the substrate.

  Derivation of M - M Equation   Leonor Michaelis and Mand L. Menton in 1913 proposed a successful explanation for the effect of substrate concentration on the enzyme activity.   According to them the enzyme E , and the substrate S combines rapidly to form a complex, the enzyme substrate complex ES. This complex then breaks down relatively and slowly to form the product P of the reaction .These sequence of reactions can be represented in the following equations o       K 1 & k 2  are the rate constants of the forward and backward reactions (step 1)   o       K 3 & k 4  are the rate constants of the forward and backward reactions respectively (step2)   This is true only for the enzyme reactions which fulfill the following conditions:   i.                    only a single substrate and a single product a...

  Enzyme Action   The molecular events that accompany the conversion of substrate into products constitute the mechanism of enzyme action. Enzyme action on its substrate results either in the formation or degradation of chemical bonds in the substrate molecules.   1.  ES Complex Formation   According to Michaelis – Menton theory, the enzyme E combines with the substrate S to form an intermediate enzyme substrate complex ES. This complex then breaks down into product P and enzyme E is regenerated. The enzyme can again combine with the fresh molecule of the substrate in similar manner. The formation of enzyme substrate complex as an intermediate during the reaction has been proved by spectroscopic studies. So, a simple enzymatic reaction might be written as   Where E, S and P represent enzyme, substrate and product respectively. ES and EP are complexes of the enzyme with substrate and product respectively. At the end of the reaction along with the required pr...

  Enzyme Inhibitor - Concepts   The rates of enzyme catalysed reactions are decreased by specific inhibitors. Inhibitors are compounds that combine with enzymes and prevent enzyme and substrate from forming ES complex. The toxicity of many compounds such as hydrogen cyanide and hydrogen sulphide results from their action as enzyme inhibitors. Many drugs also act to inhibit specific enzymes. Thus, knowledge of enzyme inhibitors is vital to understand drug action and toxic agents. Compounds which convert the enzymes into inactive substances and then adversely affect the rate of enzyme catalysed reactions are called as enzyme inhibitors. Such a process is known as enzyme inhibition. Two broad classes of enzyme inhibitors are generally recognized. They are reversible and irreversible inhibitors. This depends on whether the inhibition can be reversed or not.   1. Reversible Enzyme Inhibition   A reversible enzyme inhibitor dissociates very rapidly from its target enzyme b...