A HIGH-ACTIVITY OF 3-HYDROXY-3-METHYLGLUTARYL COENZYME-A REDUCTASE INCHLOROPLASTS 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 le ading to steviol, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) redu ctase was found to be extremely (over 150-fold in the specific activit y) higher in chloroplasts of stevia leaves than the activity of Spinac ia oleracea and about 10-fold higher than that of Solidago altissima L ., which also belongs to the Compositae family. There was no differenc e in apparent K-m values for HMG-CoA and inhibitions by mevastatin bet ween the activities of thylakoid membranes from S. rebaudiana and S. a ltissima L. Those activities were almost the same level in microsomal fractions of the three plant leaves.