Regulation of Glycine Decarboxylase and l-Serine Hydroxymethyltransferase Activities by Glyoxylate in Tobacco Leaf Mitochondrial Preparations

Publisher Website
Google Scholar
Abstract
Glyoxylate at a concentration of 10 mM caused 50% inhibition of decarboxylation of 20 mM [1-14C]glycine and accompanying synthesis of serine in a mitochondria-enriched preparation from tobacco (N. tabacum cv. JOhn Wiliams Broadleaf) leaves. None of the other compounds tested including formate, acetate, oxalate, aspartate and glutamate appreciably affected activity. Occasional inhibition produced by glycolate may have resulted from residual glycolate oxidase in these preparations. Added glycoxylate was not converted to glycine in these preparations and .apprx. 98% of it could be recovered at the end of the reaction. The inhibition by glyoxylate did not result from dilution of radioactivity in the substrate. Glyoxylate also regulated synthesis of HCHO from L-serine catalyzed by L-serine hydroxymethyltransferase in mitochondrial preparations. Control of this enzyme activity by glyoxylate was complex and was characterized by enhancement of activity at low glyoxylate concentrations (< 10 mM) and inhibition by concentrations generally > 10 mM. These results define potential sites of biochemical regulation of important steps in the pathway of photorespiratory C flow and are considered in the light of other observations of effects of exogenous glyoxylate on photorespiration in leaf tissue.