Decreased Dissociation of the 3‐Methylcrotonyl‐CoA Carboxylase Complex from Achromobacter in the Presence of 3‐Methylcrotonyl‐CoA

Abstract

By inactivation of different concentrations of 3-methylcrotonyl-CoA carboxylase from Achromobucter IVS with a fixed concentration of iodoacetamide, it was demonstrated that the degree of dissociation of the complex is considerably lower in the presence of 3-methylcrotonyl-CoA. ATP did not produce this effect. This property could serve to regulate the intracellular degradation of the enzyme, if the dissociated subunits were attacked preferentially.As described in the previous article, the reassociation of the subunits of 3-methylcrotonyl-CoA carboxylase from Achromobacter IVS to form the active complex is accelerated markedly by 3-methylcrotonylCoA. This finding led us to suppose that the degree of dissociation of the complex might be smaller in the presence of 3-methylcrotonyl-CoA. We were interested in this aspect because a variable degree of dissociation dependent on the substrate concentration could serve as a regulatory mechanism for the intracellular degradation of the enzyme [l].It is known that many enzymes are more resistant to proteolytic attack in the presence of their substrates both in vivo and in vitro [2-71. In this way degradation of working enzymes is retarded. Similarly we have found that 3-methylcrotonyl-CoA carboxylase from Achromobuctev is protected from proteolytic attack in vitro by its substrate, 3-methylcrotonyl-CoA (unpublished results).A decreased degree of dissociation of the 3-methylcrotonyl-CoA carboxylase complex in the presence of 3-methylcrotonyl-CoA would support the hypothesis of Dehlinger and Scliimke [8,5], who proposed that intracellular proteolysis might take place while the proteins are dissociated. The rate of degradation would thus be regulated by the substrate concentration via a variation of the dissociation constant.

Purification and Characterization of 3-Methylcrotonyl-Coenzyme A Carboxylase from Higher Plant Mitochondria

“…However, similar findings were reported for propionyl-COA carboxylase and MCase from human fibroblast (Wolf et al, 1979). In contrast, inhibition of Achromobacter MCase by iodoacetamide was prevented by 3-methylcrotonyl-COA but not by ATP (Schiele and Stürzer, 1975), whereas inhibition of bovine kidney MCase by p-hydroxymercuribenzoate, another sulfhydryl reagent, was prevented by ATP but not by 3-methylcrotonyl-COA (Lau et al, 1980). On the other hand, bovine kidney MCase, which was inactivated by phenylglyoxal, was protected by ATE' but not by 3-methylcrotonyl-COA (Lau et al, 1980).…”