Current Topics in Cellular Regulation: Volume 24, Enzyme Catalysis and Control is a compendium of papers that discusses phosphoryl transfer reactions, the role of water on the free energy of hydrolysis of pyrophosphate, and the hormonal actions of vitamin D. Other papers describe the regulation lipid metabolism by a lipid-carrying protein, the GABA, and taurine enzymes in mammalian brain. One paper examines the role of vitamin D in the metabolism of cells, as well as in the whole animal. Upon absorption in the body, the vitamin undergoes various metabolic transformations before interacting with specific receptors, and then inducting the genome in the target tissues to generate biological and hormonal responses. Another paper notes the possibility of a genetic defect in cancer cells that results in the abnormal accumulation of sterol carrier protein (SCP) and cholesterol in vivo; and also in the inability to maintain levels of SCP or cholesterol in vitro. One paper shows that tartrate, or other organic acids, secreted into the medium by the penicillia keeps the p H in an optimal range for acid protease degradation of proteins and glycoproteins. This mechanism helps the fungus to survive in a nutrient environment (which is unbalanced with respect to an optimum C/N ratio and at a p H unfavorable to many bacteria and other life forms). Another paper proposes a model for the modulation of ATP synthetase activities and medium exchange reactions by energy input, substrate concentration, or others that affect the microenvironment of the enzyme under certain conditions. The compendium will prove beneficial to molecular biologists, general biologists, microbiologists, and biochemists.