title: Re-evaluation of the role of thiol groups in rabbit muscle aldolase A.
abstract: Exposed thiol groups of rabbit muscle aldolase A were modified by 5,5'-dithiobis(2-nitrobenzoic) acid with concomittant loss of enzyme activity. When 5-thio-2-nitrobenzoate residues bound to enzyme SH groups were replaced by small and uncharged cyanide residues the enzyme activity was restored by more than 50%. The removal of a bulky C-terminal tyrosine residue from the active site of aldolase A resulted in enzyme which was inhibited by 5,5'-dithiobis(2-nitrobenzoic) acid only by 50% and its activity was nearly unchanged after modification of its thiol groups with cyanide. The results obtained show directly that rabbit muscle aldolase A does not possess functional cysteine residues and that the inactivation of the enzyme caused by sulfhydryl group modification reported previously can be attributed most likely to steric hindrance of a catalytic site by modifying agents.
mesh_terms: D000818:Animals; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology*; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D009579:Nitrobenzoates / Q000494:pharmacology*; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000032:analysis
chemical_list: D009579:Nitrobenzoates; D013438:Sulfhydryl Compounds; D004228:Dithionitrobenzoic Acid; D005634:Fructose-Bisphosphate Aldolase