Role of phosphoenolpyruvate carboxylase in malate production by the developing barley aleurone layer

Abstract

The pathway of malate synthesis in the developing eleurone layer of barley (Hordeum vulgare L. cv. Himalaya) was investigated. Malate formation did not occur under anoxia. Labelling with [12-14C]acetate showed that the gloxylate pathway was not a significant source of malate. The partitioning of glycolytic carbon flux at the branchpoint between phosphoenolypyruvate carboxylase (PEPC, EC 4.1.1.31) and pyruvate kinase (PK, EC 2.7.1.40) was studied using [U-14C]glucose. It was concluded that in aleurone from maturing, rapidly acidifying grains the flux through the PEPC branch relative to that through PK is 3-5 times greater than in young aleurone. This increase in flux can be accounted for by a 5-fold increase in PEPC protein determined by western blotting and in PEPC activity measured in vitro.