Rabbit muscle phosphoglucose isomerase was modified with phenylglyoxal or 2,3-butanedione, the reaction with either reagent resulting in loss of enzymatic activity in a biphasic mode. At slightly alkaline pH butanedione was found to be approximately six times as effective as phenylglyoxal. The inactivation process could not be significantly reversed by removal of the modifier. Competitive inhibitors of the enzyme protected partially against loss of enzyme activity by either modification. The only kind of amino acid residue affected was arginine. However, more than one arginine residue per enzyme subunit was found to be susceptible to modification by the dicarbonyl reagents. From protection experiments it was concluded (i) that both modifiers react specifically with an arginine in the phosphoglucose isomerase active site and nonspecifically with one or more arginine residues elsewhere in the enzyme molecule, (ii) that modification at either loci causes loss of catalytic activity, and (iii) that butanedione has a higher preference for active site arginine than for arginine residues outside of the catalytic center whereas the opposite is true for phenylglyoxal.
Bibliographical noteFunding Information:
i This is paper 30 in a series of Studies on Phos-phohexose Isomerases. The work was supported in part by USPHS Research Grant AM 07203, by Biomedical Research Development Grant RR 09070, and by an award to P. Igarashi from the University of California, Riverside, Chancellor’s Patent Fund. ‘Present address: Department of Medicine, University of California, Davis Medical Center, Sacramento, Calif. 95616.