A high activity of 3-hydroxy-3-methylglutaryl coenzyme a reductase in chloroplasts of Stevia rebaudiana Bertoni

Stevia leaves (Stevia rebaudiana Bertoni; Compositae) accumulate sweet glycosides, the aglycone of which is a diterpene derivative, steviol. The activity of the rate-limiting enzyme of the isoprenoid pathway leading to steviol, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was found to be extremely (over 150-fold in the specific activity) higher in chloroplasts of stevia leaves than the activity of Spinacia oleracea and about 10-fold higher than that of Solidago altissima L., which also belongs to the Compositae family. There was no difference in apparent K-m values for HMG-CoA and inhibitions by mevastatin between the activities of thylakoid membranes from S. rebaudiana and S. altissima L. Those activities were almost the same level in microsomal fractions of the three plant leaves.