comparison of the structure and activity of cat and trout muscle pyruvate kinases

Pyruvate kinase was purified from cat and trout muscle. The enzymes had similar amino acid compositions and subunit molecular weights. In contrast to the mammalian enzyme, the trout muscle pyruvate kinase was activated by fructose 1,6‐bisphosphate. However, unlike the l‐type pyruvate kinase from mammalian liver it was not phosphorylated by cyclic‐AMP‐dependent protein kinase. The purified enzyme from cat muscle was carboxymethylated with iodo[2‐14C]acetic acid under conditions that led to the preferential labelling of one especially reactive thiol group. The labelled enzyme was cleaved with CNBr, and the radioactive fragment purified. Amino acid sequence analysis of the reactive‐thiol‐containing fragment from cat muscle pyruvate kinase showed it had the following sequence: Ile‐Gly‐Arg‐[14C]CmCys‐Asn‐Arg‐Ala‐Gly‐Lys‐Pro‐Val‐Ile‐CmCys‐Ala‐Thr‐Gln‐Hse. The corresponding peptide from trout pyruvate kinase had only one difference in its amino acid composition and the sequence around the reactive thiol was identical.