Current Topics in Cellular Regulation, Volume 18: Biological Cycles covers topics on the events of molecular biology, cellular communication, and the merging of cell structure to biochemical function. The book discusses the ornithin-urea cycle; the cycles of glutathione metabolism and transport; and the role of multienzymatic proteins in mammalian pyrimidine biosynthesis. The text also describes the significance of interconvertible enzyme cycles in cellular regulation; regulation of mammalian pyruvate dehydrogenase complex by a phosphorylation-dephosphorylation cycle; replenishment of citric acid cycle intermediates by the purine nucleotide cycle in rat skeletal muscle. The control of a secondary pathway of ethanol metabolism by differences in redox state; the role of aldolase and fructose bisphosphatase in the control of gluconeogenesis and glycolysis; and the fructose 6-phosphate/fructose 1,6-bisphosphate cycle are also considered. The book further tackles the cycles in polysaccharide biosynthesis and other important biological cycles. Biologists, microbiologists, cellular biologists, and biochemists will find the book invaluable.