COMPARATIVE STRUCTURAL PROPERTIES OF HONEYBEE AND RABBIT ALPHA-GLYCEROPHOSPHATE DEHYDROGENASES

Several structural properties of honeybee and rabbit diphosphopyridine nucleotide dependent α-glycerophosphate dehydrogenases (EC 1.1.1.8) have been compared. Both carboxypeptidase hydrolysis and hydrazinolysis were used to determine the carboxylterminal residues; 2 moles of C-terminal methionine can be released from 77,000 g of the rabbit enzyme, indicating not only that the enzyme is probably a dimer but also that its molecular weight is around 77,000 and not 60,000 g as has been suggested. At least one of the penultimate residues is histidine. The honeybee dehydrogenase contains two C-terminal alanine residues; the terminal sequence in each chain is probably -Thr-Gln-Asp-Ala. The N-terminal is apparently blocked in both proteins. Because of tryptic-resistent cores, peptide maps could not unequivocally demonstrate identical subunit amino acid sequences in either of the dehydrogenases; however, the tryptic peptide maps did not give any indication that the subunits might differ. In addition, the maps revealed that the primary sequences of the tryptic-digestible portions of the rabbit and honeybee enzymes are markedly different. Gel filtration methods demonstrated that both dehydrogenases bind 2 moles of reduced diphosphopyridine nucleotide and do not bind any free adenosine diphosphate ribose. Removal of a chromophore from the native rabbit dehydrogenase did not affect DPNH binding or the optical rotatory dispersion spectrum. The gross conformations of the rabbit and honeybee enzymes, as evidenced by optical rotatory dispersion in the region from 225 to 470 mμ, are very similar. The average hydrophobicity for the rabbit, honeybee, and rat enzymes was calculated from the known amino acid compositions; this value is essentially identical in all three cases. The results reveal that honeybee and rabbit α-glycerophosphate dehydrogenases share several similar properties, such as dimeric structure, blocked N-terminals, DPNH binding, optical rotatory dispersion, and hydrophobicity. There are, however, other properties which differ markedly, such as C-terminal sequence and amino acid sequence as illustrated by tryptic peptide maps. © 1969, American Chemical Society. All rights reserved.