Incorporation of rβ-hydroxy-rβ-methylglutaric acid into carotenoids and other ether soluble compounds in maize seedlings

3-14C-rβ-hydroxy-rβ-methylglutaric acid (HMG) was effectively incorporated into isoprenoids by excised etiolatcd shoots as well as by the cell-free extracts of maize. The rate of incorporation indicated that HMG was not degraded to acetate or acetoacetate before entering the isoprenoid pathway. HMG and HMG-CoA were equally incorporated by the soluble extract into carotenoids indicating that, in addition to HMG-CoA reductase (EC.1.1.1.34), HMG activating enzyme was also present in the plant. The soluble system (20,000 × g fraction) showed a pH optimum of 7. Endogenous metabolites such as mevalonic acid (MVA) in the reaction mixture decreased the incorporation of HMG into isoprenoids.