Dehydrogenases

This book brings together lmportant work on the structure and function of the dehydrogenases requiring nicotinamide coenzymes. The structure and function of lactate dehydrogen- ase, alcohol dehydrogenase, and glyceraldehyde 3-phosphate dehydrogenase are compared. These are the relatively simple oligomeric dehydrogenases for which very extensive structural and mechanistic information is available. Kinetic studies are dealt with in general terms, with selected examples. Genetic and structural relationships revealed by primary structure are discussed. General features of the specificity of dehydrogen- ase reactions are described. The pyridine nucleotide - disulphide oxidoreductases exemplify a type of multicomponent enzyme complex. Lipoamide dehydrogenase, glutathione reductase, and thioredoxin reduct- ase are described and compared. The fatty acid synthesizing systems of some organ- isms are nonaggregated, whereas in other organisms they are multienzyme complexes containing, in animal tissues for example, two closely related multifunctional polypeptide chains.
The dehydrogenase activities of the fatty acid syn- thesizing systems afford many points of interest, which are described and discussed. Hydroxymethylglutaryl-CoA reductase occupies a key position in the synthesis of isoprenoid compounds, including cholesterol. It probably occurs in all forms of life; in animal cells it is a microsomal enzyme. Its properties are reviewed.