Multiple forms of adenylate kinase in pig brain

The rate of ATP formation from ADP by adenylate kinase is known to be easily followed by determination of the increase in fluorescence due to the NADPH that is formed by combined reactions of hexokinase and gluc-6-p dehydrogenase. We found that the rate of CTP formation from CDP also can be followed similarly by use of more units of hexokinase and extension of the reaction time. A crude enzyme sample containing most of the activity of adenylate kinase was prepared from pig brain and eluted from a CM-cellulose column. Enzymatic activity of ATP formation and that of CTP formation were compared for all the fractions. Two fractions were found in the eluate; one was rather specific for ADP as substrate, and the other was less specific for ADP and could form CTP at an appreciable rate.