Peptide structures of pyruvate kinase isozymes: 2. Origins of types M1 and M2 isozymes suggested from species-variations in their peptide maps.

Pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) isozymes were purified: type M1 and M2 isozymes from rat, mouse and rabbit, type M1 from bull frog and type L from rat and mouse. The amino acid composition of type M1 and M2 isozymes from various species were very similar and those of type L isozymes from rat and mouse also very similar. The NH2-terminals to type M1 and M2 from rat and mouse were (Pro-Lys-Pro-), but those of the other enzymes appeared to be blocked. The COOH-terminals of type M1 and M2 from rat, mouse and rabbit were (-Val-Pro). Comparison of tryptic peptide maps of type M1 and M2 from rat, mouse and rabbit indicated that type M1 and M2 could not be produced by post-synthesis modification, but could be encoded by different type-specific mRNAs. Comparative studies on type M1 and M2 of different species showed that type M1-specific peptide spots were highly variable, whereas type M2-specific peptide spots were highly conserved. The type L isozyme showed marked species variation, indicating that this differentiated isozyme evolved more rapidly than type M2, which may be a prototype or undifferentiated isozyme.