ARGUMENTS AGAINST A CLOSE RELATIONSHIP BETWEEN NON-PHOSPHORYLATING AND PHOSPHORYLATING GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASES

Non-phosphorylating NADP-dependent glyceraldehyde-3-phosphate dehydrog enase (GAPDH) (EC 1.2.1.9) from spinach leaves was purified to homogen eity using an improved purification procedure. Thus, a major contamina nt with molecular mass and ion-exchange properties similar to non-phos phorylating GAPDH was eliminated. Using this pure non-phosphorylating GAPDH, cofactor stereospecificity was determined by H-1 NMR. Analysis of the NADPH formed from the hydride transfer from glyceraldehyde-3-ph osphate to [4-H-2]NADP showed that the enzyme belongs to the A-stereos pecific dehydrogenase family. This stereospecificity is the same as th at described for the aldehyde dehydrogenase (ALDH) superfamily and opp osite to that of the phosphorylating GAPDH. Moreover, results from pep tide sequencing analysis suggest a similarity in sequence between the non-phosphorylating GAPDH and ALDHs. Thus, the results taken all toget her strongly suggest that non-phosphorylating GAPDH belongs to the ALD H family and has no close relationship to the phosphorylating GAPDH cl ass.