An ATP-incorporating enzyme from rat brain. I. Solubilization and requirements

Abstract

An ATP-incorporating enzyme has been solubilized from a nonnuclear particulate fraction of rat brain with the nonionic detergent Triton X-100. The enzyme activity is not affected by deoxyribonuclease or ribonuclease, and is markedly stimulated by GTP and, to a lesser extent, by the other nucleoside triphosphates. There is an absolute requirement for a heat-stable cofactor present in the same enzyme extract. This cofactor has been separated from the enzyme by means of ethanol fractionation and appears to be a compound of relatively low molecular weight since it is dialyzable and heat-stable. Its activating effect is lost after incubation with alkaline phosphatase. The product of the reaction is not hydrolyzed by ribonuclease or deoxyribonuclease but is partially degraded by phosphodiesterase. A rapid non-enzymic degradation of the product occurs in neutral or moderately alkaline conditions. A significant fraction of the fragments released by alkaline hydrolysis behaves as though they were more highly charged than ADP.