A structural study of pig liver glyceraldehyde-3-phosphate dehydrogenase.

A substantial portion of the primary structure of pig liver glyceraldehyde-3-phosphate dehydrogenase has been investigated and the results compared with those previously reported for the pig muscle enzyme. Liver and muscle glyceraldehyde-3-phosphate dehydrogenases show the same amino acid content, and the first N-terminal residues occur in the same sequence. No differences in N-terminal residues and amino acid composition have been evidenced by analysis of several tryptic peptides, which account for about 50% of the total amino acid sequence. From the electrophoretic mobilities of peptides T8 T9 and T25 it is concluded that residues Asp 60, Asp 67 and Glu 220 in the reported sequence of the pig muscle enzyme must be present as amides in the liver enzyme. The NAD+ content was found to be 2 mol per tetramer, while higher values have been reported for the muscle enzyme from various mammalian sources. The reactivity of lysyl side chains towards pyridoxal 5'-phosphate has been examined: the results indicate that Lys 212 is the main site reacted in fully inactivated pig liver holoenzyme. A similar result has been found for rabbit muscle apoenzyme, whereas rabbit muscle holoenzyme reacts at Lys 212 and 191.

Extended amino acid sequences around the active-site lysine residue of class-I fructose 1,6-bisphosphate aldolases from rabbit muscle, sturgeon muscle, trout muscle and ox liver.

1. Amino acid sequences covering the region between residues 173 and 248 [adopting the numbering system proposed by Lai, Nakai & Chang (1974) Science 183, 1204-1206] were derived for trout (Salmo trutta) muscle aldolase and for ox liver aldolase. A comparable sequence was derived for residues 180-248 of sturgeon (Acipenser transmontanus) muscle aldolase. The close homology with the rabbit muscle enzyme was used to align the peptides of the other aldolases from which the sequences were derived. The results also allowed a partial sequence for the N-terminal 39 residues for the ox liver enzyme to be deduced. 2. In the light of the strong homology evinced for these enzymes, a re-investigation of the amino acid sequence of rabbit muscle aldolase between residues 181 and 185 was undertaken. This indicated the presence of a hitherto unsuspected -Ile-Val-sequence between residues 181 and 182 and the need to invert the sequence -Glu-Val- to -Val-Glx- at positions 184 and 185. 3. Comparison of the available amino acid sequences of these enzymes suggested an early evolutionary divergence of the genes for muscle and liver aldolases. It was also consistent with other evidence that the central region of the primary structure of these enzymes (which includes the active-site lysine-227) forms part of a conserved folding domain in the protein subunit. 4. Detailed evidence for the amino acid sequences proposed has been deposited as Suy Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.