The Regulation of Synthesis of Chloroplastic and Cytosolic Isoenzymes of Phosphoglycerate Kinase in Barley
In photosynthetic eukaryotes distinct isoenzymes of phosphoglycerate kinase (PGK EC 18.104.22.168) occur in chloroplasts and cytosol. The chloroplast isoenzyme is the second enzyme of the C3 photosynthetic carbon pathway and is also considered to function in glycolysis by which substrates for fatty acid synthesis are produced. The cytosolic isoenzyme participates in both glycolysis and gluconeogenesis. Both isoenzymes are involved in the regulation of carbon partitioning between starch and sucrose and in the triose phosphate/phosphoglycerate shuttle by which phosphorylating and reducing power are transported across the chloroplast envelope via the phosphate translocator. Both isoenzymes are coded by the nuclear genome and synthesized on cytoplasmic ribosomes (1). In green barley leaves the plastid: cytosol isoenzyme ratio is 90: 10 (2), but can vary from species to species and from tissue to tissue within a species. In this paper we describe the developmental changes in the activities of PGK isoenzymes during leaf growth.
KeywordsGlutamine Synthetase Continuous Illumination Phosphoglycerate Kinase Chloroplast Envelope Golden Promise
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