Abstract
1. A procedure for preparing crystalline 3-phosphoglycerate kinase from rabbit or pig skeletal muscle is presented. 2. The preparation phosphorylates up to 975μmoles of 3-phosphoglycerate/min./mg. at 30° and is not contaminated with myokinase. 3. The enzyme has an estimated molecular weight of 36500±1000, and contains three residues each of tyrosine and tryptophan. 4. The preparation is suitable for use in the enzymic procedures for determining ATP, phosphocreatine and 3-phosphoglycerate.