Abstract l-Glycerol-3-phosphate:NAD oxidoreductase (EC 1.1.1.8) from rabbit skeletal muscle obtained commercially in several separate lots was purified and examined for absence of contaminating proteins. Amino acid analysis showed 3 tyrosine, 2 tryptophan, 7 arginine, 7 histidine, 9 cysteine or half-cystine, and 22 lysine residues per minimal molecular weight which was 30,133. Peptide mapping of trypsin and of trypsin-chymotrypsin digests of the 14C-S-carboxymethylated enzyme under a variety of conditions showed 3 tyrosine, 2 tryptophan, 7 arginine, 5 or 6 histidine, 9 or 10 14C-S-carboxymethylcysteine, and 28 to 31 tryptic peptides. Molecular weight estimation on Sephadex G-75, G-100, and G-200 gave values ranging from 61,000 to 66,000. An s20,w of 4.2 was obtained by sedimentation velocity and by sucrose gradient ultracentrifugation. Equilibrium ultracentrifugation by the LaBar method gave a molecular weight of 66,000 to 69,000. These chemical studies in conjunction with the physical determinations show that the enzyme has a molecular weight of 60,266 (excluding the nonprotein component) and is composed of subunits that are indistinguishable by peptide mapping. Thus, the substantial difference in molecular weight that was previously indicated between the enzyme from rabbit muscle as compared to that from rat or bee muscle does not exist. The possibility that l-glycerol-3-P dehydrogenase and triose phosphate isomerase may be related in primary structure is suggested based on substrate specificity, molecular weight, and difference index between their propsective amino acid compositions, but definitive evidence is not yet available.
No takes yet. Share an insight, caveat, or question.
Fondy et al. (1969) studied this question.