Glyoxylate Reductase Activity in Pea Leaf Protoplasts Nucleotide Specificity and Subcellular Location

Abstract

Summary Protoplasts purified from leaves of Pisum sativum L. were lysed and fractionated under conditions of low chloroplast breakage in order to determine the subcellular distribution of NADPH- and NADH-dependent glyoxylate-reductase activities. Results from rate-zonal sedimentation and sucrose-gradient experiments demonstrated that a high proportion of the glyoxylate-reducing activity was in the supernatant fraction, where NADPH was the preferred reductant. Significant but much lower (on a chlorophyll basis) glyoxylate-reductase activity was also associated with the chloroplast fraction. Latency was demonstrated for both the NADH and NADPH-dependent chloroplastic activities, confirming their presence within the organelles. The peroxisome-enriched fraction, which was high in NADH-hydroxypyruvate reductase, showed no significant glyoxylate-reducing activity with 1 mM glyoxylate. It is postulated that the cytosolic and chloroplastic glyoxylate-reductase enzymes could readily convert to glycolate any glyoxylate leaked or exported from peroxisomes, thereby counteracting glyoxylate accumulation.