Selenium-dependent enzymes from protein

Although formate dehydrogenase activity is widely distributed in bacteria, only E. coli and several anaerobic organisms are known to possess the selenium-dependent form of the enzyme. These are complex enzymes that from E. coli, for example, has an MW of approximately 600,CKX) and contains 4 hemes, 4 equivalents of molybdenum, 56 of nonheme iron, 53 of acid labile sulfur, and 4 of selenium. The enzyme complex contains three types of subunits with MW of IIO.CKK), 32,000, and 20,(XK). Each of the four 110,000-Da subunits contains one equivalent of selenium which is present as selenocy-steine. More detailed analysis has focused on the incorporation of selenocysteine into this protein than into any other selenoproteins . ... 

Molybdoenzymns At present, 6 oligomeric oxi-doreductases are known, which contain Mo as an essential constituent 1. Nitrogenase (see) 2. Nitrate reductase, EC 1.6.6.3 (see) 3. Xanthine oxidase, EC 1.2.3.2 (see), from animals and bacteria 4. Aldehyde oxidase, EC 1.2.3.1 from animal liver, which catalyses the reaction R-CHO + HjO R-COOH + 2H + 2e 5. Sulfite oxidase, EC 1.18.3.1 from mammalian and bird liver (Af, 114,000 2 subunits), which catalyses the reaction S03 + HjO-> SO/ + 2H + 2e this enzyme also contains a b5-like cytochrome and passes electrons directly to cytochrome c in the respiratory chain and 6. Formate dehydrogenase, EC 1.2.1.2, a membrane-bound protein from E. coli, containing one atom each of molybdenum and selenium, one heme group and nonheme iron-sulfur centers. It is NAD -dependent and catalyses the reaction HCOO + NAD CO2 -I- NADH. 

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