Brain phosphorylation and decarboxylation of mevalonic acid in the neonatal chick

The three enzymes which catalyze mevalonic acid (MVA) phosphorylation and decarboxylation in neonatal chick brain are essentially located in the soluble fraction. The specific activity of pyrophosphomevalonate decarboxylase was the lowest of the three mevalonate-metabolizing enzymes. The rate of MVA phosphorylation and decarboxylation as a function of MVA concentration was studied. The apparent Km value of mevalonate kinase for MVA was 255 mumol/l. All three enzymes in chick brain showed a specific requirement for ATP for optimal activity. The effect of different Mg2+ concentrations was also studied. Mevalonate kinase and phosphomevalonate kinase showed maximal activity at pH 9.2 whereas pyrophosphomevalonate decarboxylase activity was highest at about pH 6.5--6.7.