MPSC Notes - Enzyme Activity Parts - III

21. What is the relationship between vitamins and enzyme cofactors?

Many vitamins are enzyme cofactors that cannot be synthesized by the organism and must be obtained from the diet.

22. For the enzymatic reaction what is the effect of a substance with the same spatial conformation as an enzymatic substrate? How is this type of substance known?

Substances that “simulate” substrates can bind to the activation center of enzymes thus blocking the true substrates to bind to these enzymes and paralyzing the enzymatic reaction. Such “fake substrates” are called enzyme inhibitors.

The binding of enzyme inhibitors to enzymes can be reversible or irreversible.

Many medical drugs, for example, some antibiotics, antivirals, antineoplastics, antihypertensives and even sildenafil (trade name Viagra), are enzyme inhibitors that block enzyme activity.

23. What is the action mechanism of the antibiotic penicillin?

Penicillin, discovered by the Scottish doctor Alexander Fleming in 1928, is a drug that inhibits enzymes necessary for the synthesis of peptidoglycans, a constituent of the bacterial cell wall. With the inhibition the bacterial population stops growing because there is no new cell wall formation.

Fleming won the Nobel prize in Medicine for the discovery of penicillin.

24. What is the action mechanism of the antiretroviral drugs called protease inhibitors which are used against HIV infection?

Protease inhibitors are some of the antiretroviral drugs used to treat HIV infection. Protease is an enzyme necessary for the assembling of HIV after the synthesis of its proteins within the host cell. The protease inhibitor binds to the activation center of the enzyme blocking the formation of the enzyme-substrate complex and the enzyme activity thus impairing the viral replication.

25. What are allosteric enzymes?

Allosteric enzymes are those that have more than one activation center and to which other substances, called allosteric regulators, bind.

Allosteric regulators can be allosteric inhibitors or allosteric activators. The interaction between an allosteric enzyme and the allosteric inhibitor disallows the binding of the substrate to the enzyme. The interaction between the allosteric enzyme and the allosteric activator allows the binding of the substrate to the enzyme and sometimes increases the affinity of the enzyme for the substrate. This regulatory phenomenon of the enzyme activity is called allosterism.

26. What are zymogens?

Zymogens, or proenzymes, are enzymes secreted in inactive form. Under certain conditions a zymogen shifts to the active form of the enzyme. Zymogen secretions in general happen because the enzyme activity can harm the secretory tissue.

For example, the pepsinogen secreted by the stomach becomes active under acid pH turning into the enzyme pepsin. Other well-known zymogens are trypsinogen and chymotrypsinogen, enzymes that are secreted by the exocrine pancreas and which become trypsin and chymotrypsin respectively.

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