Purification and properties of pig liver and muscle enolases

Abstract

Enolases (2-phospho-d-glycerate hydrolase, EC 4.2.1.11) were purified from both pig liver and muscle. Graphs of InC vs.r ² from sedimentation equilibrium experiments are linear, which suggests homogeneous preparations of liver and muscle enolases. From these data the molecular weight of liver enolase is calculated to be approximately 92,000 D and that of muscle enolase to be approximately 85,000 D. SDS-PAGE experiments give a molecular weight value of 46,000 D for liver enolase and a value of 44,000 D for muscle enolase. These molecular weight values for liver and muscle enzymes are within the range for other enolases and show that both of these pig enolases are dimers. Amino acid composition data support the sedimentation equilibrium data and also give a smaller molecule weight (84,968 D) for muscle enolase compared to that of the liver enzyme (89,021 D). The two enzymes differ in their content of lysine [liver enolase (L)=94 residues, muscle enolase (M)=68 residues], histidine (L=13, M=21), serine (L=53, M=36), proline (L=52, M=34), and cysteine (L=4, M=21). Partial specific volumes of 0.737 ml/g for liver enolase and 0.735 ml/g for muscle enolase were calculated from the amino acid composition data. Pig liver and muscle enolases differ radically in their isoelectric points (pI=6.4–6.5 for liver enolase, and pI=8.8–9.0 for muscle enolase), and in their degree of inactivation by 750 mM LiCI (liver enolase is inactivated to a greater degree than the muscle enolase). Despite these physical and chemical differences, the kinetic constantsK _M values for Mg²⁺, 2-phosphoglyceric acid, and phospho(enol)pyruvate appear not to be significantly different for these two forms of enolase. The physical, chemical, and kinetic data for pig liver and muscle enolases are compared to similar data for pig kidney enolase.