3-HYDROXY-3-METHYLGLUTARYL-COENZYME, A SYNTHASE IN HEVEA-BRASILIENSIS

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase activity in r ubber (Hevea brasiliensis) latex and in fractions obtained by centrifu gation was determined using a radiochemical method. The enzyme was fou nd in both C-serum and bottom fraction, but most was in the C-serum. H evea brasiliensis leaves showed very low enzyme activity. HMG-CoA synt hase in C-serum was found to be free of HMG-CoA lyase. The enzyme in C -serum was stable at -70 degrees. The formation of HMG-CoA did not dep end on a supply of exogenous acetoacetyl-CoA, and the rate of formatio n was increased as the concentration of acetyl-CoA was increased. The K-m for acetyl-CoA was 9 mM. The enzyme in C-serum was inhibited by se veral divalent cations, p-chloromercuribenzoate and dithiothreitol. Di urnal variation in the activity of the enzyme in both C-serum and extr acts of leaves was observed. A positive correlation between the enzyme activity and the rubber content of the latex (correlation coefficient of + 0.81) suggests that the enzyme regulates the synthesis of rubber in the latex.