Inactivation of crystalline tobacco ribulosebisphosphate carboxylase by modification of arginine residues with 2,3-butanedione and phenylglyoxal.

Crystalline tobacco ribulosebisphosphate carboxylase (3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39) is rapidly and completely inactivated by 2,3-butanedione in borate buffer or phenylglyoxal, reagents which are highly specific for the modification of arginine residues. Inactivation by phenylglyoxal is enhanced in Bicine buffer and partially reversible, whereas inactivation by butanedione is markedly enhanced in borate buffer, irreversible in the presence of borate and partially reversed upon complete removal of borate and excess reagent. When the modification reaction is performed in the presence of various ligands, only the substrate ribulosebisphosphate and the diphosphorylated competitive inhibitor sedoheptulosebisphosphate protect against inactivation. Loss of carboxylase activity is directly proportional to incorporation of [14C]phenylglyoxal until about 15% of the initial activity remains. Extrapolation to zero activity suggests that inactivation by [14C]phenylglyoxal correlates with the modification of three arginine residues per 69 000 dalton protomer. Complete protection by ribulosebisphosphate or sedoheptulosebisphosphate correlates with the shielding of 1-2 (1.27 +/- 0.25) essential arginyl groups per protomer, which are located within the 55 000 dalton catalytic subunits of the protein. Similarly, amino acid analyses of acid hydrolysates of the butanedione- or phenyl-glyoxal-inactivated and substrate-protected enzymes suggest that complete protection by ribulosebisphosphate correlated with the shielding of 1.9-2.4 arginine residues per protomer. However, modification of the control and substrate-protected enzymes are these arginine-selective alpha-dicarbonyls does not alter modulation by anionic effectors.