Inactivation of glyceraldehyde 3-phosphate dehydrogenase

Abstract

Enzymatic activity and physical chemical properties have been determined for yeast glyceraldehyde 3-phosphate dehydrogenase (GPD) exposed to low and high pH. Inactivation of the enzyme is rapid below pH 4.5 and above pH 11, and is accompanied by a decrease in sedimentation constant resulting in large part from dissociation into its constituent subunits. Both the sedimentation and optical rotation dispersion behavior of inactivated GPD indicates that a drastic unfolding of the subunit has probably occurred. The ORD parameters of native yeast GPD are comparable to those previously reported for the apo-muscle enzyme and suggest a similarity in their secondary and tertiary structures. The relative magnitude of these parameters suggests that GPD contains ordered structural elements other than helix and random chain. The drastic changes for a 0 and b 0 observed in the regions of inactivation of yeast GPD appear to be due largely to “melting out” of these nonhelical regions. Acid inactivation appears to give as disordered a structure as is observed on urea denaturation, while the process at high pH appears to be less complete.