The structure and catalytic role of Pyridine enzymes

Pyridine enzymes consist of apoenzyme and coenzyme as NAD or NADP. NAD is nicotinamide adenine dinucleotide. NADP is nicotinamide adenine dinucleotide phosphate. Both of them consist of adenine, 2 riboses, 2 phosphates and nicotinamide (vitamin PP). NADP also contains additional phosphate.

NADP-dependent pyridine enzymes take part in synthetic processes (e.g. biosynthesis of free fatty acids etc):

S+NADPH2àSH2+NADP

They occur in cytosol. NAD_dependent pyridine enzymes are contained in mitochondrias and take part in BO by dint of dehydrogenation of substrates. Hence they are primary DH-ases:

SH2+NADàS+NADH2+energy

NADH2 are oxidized by FP (with FMN). Some substrates are oxidized by FP with coenzyme FAD.

The structure and catalytic role of Flavin enzymes (FP)

Flavin enzymes consist of apoenzyme and coenzyme as FMN and FAD. FMN is flavinmononucleotide (v.B2+H3PO4); FAD is flavinadeninedinucleotide (FMN + AMP).

Flavin ring carries out a catalytic role.

FP with FAD are primary DH-ases because they oxidize substrates, e.g. succinate dehydrogenase (SDH) oxidizes succinic acid to fumaric acid. FPH2 are oxidized by CoQ (Ubiquinone). Some FP, e.g. Xanthine oxidase etc may be oxidized by molecular oxygen, i.e. they possess the autooxidability: FPH2 + O2 = FP + H2O2

The structure and catalytic role of Ubiquinone

Coenzyme Q is so named because its apoenzyme hasn’t been found. The term “Ubiquinone” is from “ubiquity” – it occurs in all types of cells:

Reduced ubiquionone is oxidized without any enzymes. Hydrogen atoms are just broken up on protons and electrons. Protons are used in formation of endogenic water. Electrons are carried on cytochromes

<== попередня сторінка	\|	наступна сторінка ==>
The structure and catalytic role of decarboxylases of amino acids	\|	The structure, catalytic role and representatives of Cytochromes

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