Plant pyruvate kinase

Pyruvate kinase is an important enzyme of glycolytic pathway that also functions in providing carbon skeleton for fatty acid biosynthesis. It has been purified to near homogeneity from Ricinus communis, Selenastrum minutum, Cynodon dactylon, Brassica campestris and R napus, and characterised. Partially purified preparations are reported from several other sources. A phosphoenolpyruvate (PEP) phosphatase accompanies pyruvate kinase. In plants, two isozymes of pyruvate kinase are reported, namely cytosolic and plastidic. Isoforms of cytosolic pyruvate kinase have also been reported from spinach. In most cases pyruvate kinase is a tetrameric protein and the molecular mass lies between 200 to 250 kDa. The pH optimum is in the range of 6.2 to 7.5. It requires both Mg2+ and K+ for maximum activity. ATP, citrate, and oxalate inhibit pyruvate kinase in most cases. A sequential compulsory ordered mechanism of binding of substrates to the enzyme has been proposed.