Incorporation of 18O into oxalic, l-threonic and l-tartaric acids during cleavage of l-ascorbic and 5-keto- d-gluconic acids in plants

Abstract

l-[1,6- 14C]Ascorbic acid was administered to young leaves of Pelargonium. 5-Keto- d-[1- 14C]gluconic acid, a metabolic product of l-[1- 14C]ascorbic acid in grape, was supplied to young leaves of Pelargonium, parsley, bean and grape in the presence of 18O 2 or H 2 18O. From the 18O incorporated into oxalic and l-threonic acids, which were C2/C3 cleavage products of l-ascorbic acid, and into l-tartaric acid, which was a C4/C5 cleavage product of 5-keto- d-gluconic acid, the number of oxygen atoms incorporated into the respective organic acids was calculated. The data strongly suggest that a cleavage mechanism of C2/C3 of l-ascorbic acid involves both oxygenase and hydrolase reactions but that cleavage of C4/C5 of 5-keto- d-gluconic acid is due only to hydrolase.