Multienzyme systems, hydroxylating

Heme coenzymes, iron-sulfur clusters, flavin coenzymes, and nicotinamide coenzymes cooperate in multienzyme systems to catalyze the chemically remarkable hy-droxylations of hydrocarbons such as steroids (chapter 20). In these hydroxylation systems, the heme proteins constitute a family of proteins known as cytochrome P450, named for the wavelength corresponding to the most intense absorption band of the carbon monoxide-liganded heme, an inhib-... 

Heme coenzymes participate in a variety of electron-transfer reactions, including reactions of peroxides and 02. Iron-sulfur clusters, composed of Fe and S in equal numbers with cysteinyl side chains of proteins, mediate other electron-transfer processes, including the reduction of N2 to 2 NH3. Nicotinamide, flavin, and heme coenzymes act cooperatively with iron-sulfur proteins in multienzyme systems that catalyze hydroxylations of hydrocarbons and also in the transport of electrons from foodstuffs... 

O-acetylation has also been demonstrated by Schauer (1970c,t/) using slices of horse and bovine submaxillary gland. Acetyl-CoA appears to be the donor, and again free NAN or its 9-phosphate ester or CMP-NAN appear to be the acceptors. In a later paper (Schauer and Wember, 1971), both hydroxylation and O-acetylation of membrane-bound polymer NAN was demonstrated. Until these enzyme systems are solubilized and purified, it is not clear at what level derivatization (hydroxylation and O-acetylation) occurs. Schauer (1972) has presented a model which involves specific enzymes which catalyze transfer of CMP-NAN to polymers. All of the enzymes are arranged in a multienzyme membrane-bound complex. This interesting model awaits experimental verification. 

---