D-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE - PROPERTIES OF THE ENZYME-MODIFIED AT ARGININE RESIDUES

Examination of the properties of Escherichia coli and rabbit muscle D- glyceraldehyde-3-phosphate dehydrogenases (GPDHs) modified by 2,3-buta nedione has shown that both tetrameric enzymes are stabilized, on sele ctive modification of arginine residues (probably Arg 231), in an asym metric state with only two active centers capable of performing the de hydrogenase reaction. The functionally incompetent active centers can be alkylated by iodoacetate or iodoacetamide in the case of E. coli en zyme, but are inaccessible for these reagents in the case of rabbit mu scle D-GPDH. These results are consistent with the idea that the two h omologous enzymes share common principles of the protein design, but d iffer somewhat in their active centers geometries. Modification of the arginine produces marked changes in the shape of the charge transfer complex spectrum in the region of 300-370 nm, suggestive of the altera tions in the microenvironment of the nicotinamide ring of NAD(+), alth ough the coenzyme binding characteristics remain largely unaltered. On arginine modification, the enzyme becomes insensitive to the effect o f AMP on the kinetic parameters of p-nitrophenyl acetate hydrolysis re action.