Pyruvate kinase from Trichomonas vaginalis, an allosteric enzyme stimulated by ribose 5-phosphate and glycerate 3-phosphate

Abstract

Trichomonas vaginalis pyruvate kinase was purified over 1750 fold to a specific activity greater than 100 mumol min-1 (mg protein)-1. The enzyme is a tetramer of M(r) 266,000, consisting of subunits of M(r) 53,000 and 56,000 in equivalent amounts. Its activity was dependent on the presence of magnesium but was not stimulated by potassium or ammonium. The enzyme exhibited positive cooperativity towards phosphoenolpyruvate and was inhibited by inorganic phosphate, which increased the sigmoidicity of the saturation curve for phosphoenolpyruvate without affecting maximal activity. It was heterotropically stimulated by ribose 5-phosphate and glycerate 3-phosphate, not previously known to act on eukaryotic pyruvate kinases, but was unaffected by known effectors of most pyruvate kinases, including fructose 1,6-bisphosphate and fructose 2,6-bisphosphate.