Subunit structure of rabbit muscle pyruvate kinase.

Peptide mapping of rabbit muscle pyruvate kinase following tryptic digestion gave one-quarter the number of ninhydrin-reactive peptides, arginine-containing peptides, and tryptophan-containing peptides expected from the amino acid composition. Sedimentation velocity studies and disc gel electrophoresis of the enzyme subunits formed in 4 M urea and having one-quarter of the initial molecular weight gave no indication of more than one species. These results indicate that pyruvate kinase contains four highly similar, although not necessarily identical, subunits. About 4 moles of acetate were liberated per mole of enzyme upon acid hydrolysis, and differential hydrazinolysis indicated that these are probably present in the protein as amino acetyl groups. No free amino-terminal residues could be detected. Whereas the 7.3 S species formed in 2 M urea and having one-half of the initial molecular weight retains catalytic activity, the 2.0 S species formed in 4 M urea is inactive. Conditions are described under which the subunits undergo reassociation to a form having the sedimentation constant (10.0 S) and most of the catalytic activity of the native enzyme.