THE MASKED CYSTEINE RESIDUES IN METHYLMALONYL-COA MUTASE FROM PROPIONIBACTERIUM-SHERMANII ARE ESSENTIAL FOR CATALYTIC ACTIVITY

Two masked cysteine residues have been reported in methylmalonyl-CoA m utase from Propionibacterium shermanii, Cys-535 in the alpha-subunit a nd Cys-517 in the beta-subunit, which are revealed only after reductio n of the denatured enzyme with dithiothreitol, It has been postulated that these residues are involved in disulphide linkages to unknown thi ols of low M(r). These two masked cysteine residues have been changed to an alanine, individually, Both the mutants, C535 alpha A and C517 b eta A, mere inactive. This shows that both these residues are essentia l for catalytic activity.