3‐Phosphoglycerate Kinase from Rabbit Sceletal Muscle and Yeast

Phosphoglycerate kinase, isolated from rabbit muscle in highly purified crystalline form, was compared in terms of chemical, physical and kinetic properties to yeast phosphoglycerate kinase. A summary of the data is presented. Both proteins are composed of a single polypeptide chain, and in electrophoresis only one band was found. The N‐terminus is masked. The C‐terminal amino acid of the muscle enzyme is valine. Muscle and yeast enzyme have nearly identical molecular weights, Michaelis‐Menten constants, optimal pH values and V max . On the other hand, they differ significantly in their amino acid composition, especially in the content of sulfur and aromatic amino acids, in electrophoretic mobility and in heat stability. The muscle enzyme has an essential SH group. The single SH group of the yeast enzyme is apparently without importance for enzyme activity. Differences in the same direction as those observed with yeast and muscle phosphoglycerate kinase are discussed in connection with other glycolytic enzymes from the same organisms.