EVIDENCE OF ESSENTIAL ARGINYL RESIDUES IN RABBIT MUSCLE PYRUVATE-KINASE
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1979
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Abstract
Rabbit muscle pyruvate kinase [EC 2.7.1.40] is inactivated by 2,3-butanedione in borate buffer. The inactivation follows pseudo-1st-order kinetics with a calculated 2nd-order rate constant of 4.6/M per min. The modification can be reversed with almost total recovery of activity by elimination of the butanedione and borate buffer, suggesting that only arginyl groups are modified. This result agrees with the loss of arginine detected by amino acid analysis of the modified enzyme. Using the kinetic data, it was estimated that the reaction of a single butanedione molecule/subunit of the enzyme is enough to completely inactivate the protein. The inactivation is partially prevented by phosphoenolpyruvate in the presence of K+ and Mg2+, but not by the competitive inhibitors lactate and bicarbonate. These findings point to an essential arginyl residue being located near the phosphate binding site of phosphoenolpyruvate.