D-glyceraldehyde-3-phosphate dehydrogenase

Examination of the properties ofEscherichia coli and rabbit muscle D-glyceraldehyde-3-phosphate dehydrogenases (GPDHs) modified by 2,3-butanedione has shown that both tetrameric enzymes are stabilized, on selective modification of arginine residues (probably Arg 231), in an asymmetric state with only two active centers capable of performing the dehydrogenase reaction. The functionally incompetent active centers can be alkylated by iodoacetate or iodoacetamide in the case ofE. coli enzyme, but are inaccessible for these reagents in the case of rabbit muscle D-GPDH. These results are consistent with the idea that the two homologous enzymes share common principles of the protein design, but differ 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 alterations in the microenvironment of the nicotinamide ring of NAD⁺, although the coenzyme binding characteristics remain largely unaltered. On arginine modification, the enzyme becomes insensitive to the effect of AMP on the kinetic parameters of p-nitrophenyl acetate hydrolysis reaction.