Effects of insulin and of glycerol in vitro on the incorporation of [carboxy-14C] acetate into the fatty acids of lactating mammary gland slices with special reference to species differences.

activators though less so than magnesium. Potassium ions are inactive in this respect. 3. The pH optimum of the enzyme for the forward reaction, i.e. the splitting of phosphocreatine in the presence of adenylic acid lies in the range of 5*9-7; phosphocreatine is split optimally at the same pH range when adenosinediphosphate is used as the phosphate acceptor. 4. Preparations from brain also catalyse the synthesis of phosphocreatine from creatine and adenosinetriphosphate above pH 8-2. 5. None of the drugs of central action which were examined had any significant effect on the activity of the enzyme. Iodoacetate inhibited it completely above a concentration of 05 mm and fluoride to a much less marked degree. I wish to thank Dr McIlwain for having suggested the problem and for many helpful discussions.