Question

1)Summarise the structural features and function of enzyme-bound, flavin cofactors

2)Describe with examples, the relation between cofactors and vitamins.

3)Understand the role of metal ion cofactors, and relate to the requirement for mineral nutrients.

Answer 1

Ans .(1) Many enzymes use one or more cofactors, such as biotin , heme, or flavin. These cofactors may be bound to the enzyme in a noncovalent or covalent manner. Although most flavoproteins contain a noncovalently bound flavin cofactor (FMN or FAD) , a large number have these cofactors covalently linked to the polypeptide chain.

Flavins are a ubiquitous class of redox - active coenzymes that are able to catalyze a number of different chemical reactions when bound to apoproteins. They play an important role in dehydrogenation and hydroxylation reactions, in oxygen activation, and in one -and two- electron transfer processes from and to redox centers.

Ans .(2) Nonprotein components of certain enzymes are called cofactors. If the cofactor is organic , then it is called a coenzyme. Coenzymes are relatively small molecules compared to the protein part of the enzyme and many of the coenzymes are derived from vitamins.

Vitamins can serve as precursors to many organic cofactors (e.g. Vitamins B1, B2 , B6 ,B12, niacin , folic acid ).

Ans (3) Metal ion cofactors have varied roles to enhance the catalytic efficiency of enzymes in hydrolytic reactions, including facilitate substrate binding, gathering / template effects, function as an electrostatic catalyst (carbonyl polarization and transitional state stabilization).

Zinc (metal ion cofactor ) is needed for growth and for maintenance of the immune function , which enhances both the prevention of and recovery from infectious diseases.