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The structure, catalytic role and representatives of Cytochromes

Cytochromes are two-component enzymes. They consist of apoenzyme and coenzyme as heme. Cytochromes are divided into 4 groups – A, B, C, D. each group is subdivided into subgroups, so group A includes Cyta and Cyta3; group B includes Cytb and Cytb5; group C includes Cytc and Cytc1. Cytochromes of group D occur in plants. Cytochromes of each group differ from each other by structure of heme. Cytochromes of subgroups differ from each other by structure of apoenzyme, i.e. they contain the same hemes.

Cytochromes of group B have got a heme which looks like heme of hemoglobin and myoglobin:

1,3,5,8-tetramethyl-2,4-divinyl-6,7-dipropionic acid iron porphin

The heme of cytochromes of group C is: 1,3,5,8-tetramethyl-2,4-diethyl-6,7-dipropionic acid iron porphin

The heme of cytochromes of group A is: 1,3-dimethyl-2-radical-4-vinyl-8-formyl-6,7-dipropionic acid iron porphin

The iron of hemes of cytochromes may be 3+ and 2+:

+e

Cyt (Fe3+) --------------------------------------------à Cyt (Fe2+)

(ferri) ß-------------------------------------------- (ferro)

– e

ferri form of cytochrome is oxidized. Ferro form of cytochrome is reduced one.

The subsequence of cytochromes in BO depend on their oxidative-reductive potential. They are located according increase of their potential: cytbà cytc1àcytcàcytaàcyta3àO2

The structure and catalytic role of Catalase and peroxidases

Catalase and peroxidases consist of apoenzyme and coenzyme as heme. Apoenzyme is represented by 1 polypeptide chain. Heme is the same of heme of hemoglobin and myoglobin but iron has 3 valency. Catalase contains 4 hemes whereas peroxidases contain 1 heme.

Catalase catalyzes the next reaction: 2H2O2 à 2H2O + O2

Peroxidases catalyze the reaction: H2O2 à H2O + [O]

The structure and catalytic role of oxygenases

Oxygenases consist of apoenzyme and coenzyme as vitamin C (ascorbic acid).

MOG oxidize substrates by dint of inclusion of atom of oxygen. This results in formation of hydroxylated product or product like SO: S+O2+NADPH2àSO(H)+H2O+NADP

DOG include molecule of oxygen in substrate. This results in cleavage of double bond:

S+O2àSO2 (e.g. formation of vitamin A from carotene and formation of dioxide of oleinic acid).

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