The complete amino acid sequence of cat muscle pyruvate kinase has been determined and fitted to the 2.6 A resolution electron density map. Residues in the active site region are highly conserved in the cat muscle, chicken muscle, rat liver and yeast enzymes. The enzyme‐bound magnesium, which is essential for activity, interacts with the side chain of glutamate‐271 and with two main carbonyl groups. Lysine‐269 is the probable acid/base catalyst responsible for the interconversion of pyruvate and enolpyruvate. A possible binding site for the essential monovalent cation is proposed.

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