On the role of magnesium in the reaction of the pyruvate kinase from Salmonella typhimurium.

The kinetics of the two purified forms of pyruvate kinase from Salmonella typhimurium LT-2 were studied in assays at pH 6.8 where the relationships between the initial velocities of the catalysed reactions and Mg2+ are non-hyperbolic. The analysis show that Mg2+ display positive homotropic interactions in their binding behaviour with Hill coefficient values of 2.5 and 1.2 for the form I and II, respectively. The binding sites of the cation to the pyruvate kinases seem to be independent to those for phosphoenolpyruvate and adenosine 5'-diphosphate; changes in the magnesium concentration might be of physiological significance in relation to a rapid regeneration of adenosine 5'-triphosphate by means of the pyruvate kinase reaction.