Calcium-Binding Protein Isolated from Rat Liver Cytosol Reverses Activation of Pyruvate Kinase by Ca²⁺

抄録

The effect of a calcium-binding protein (CaBP) isolated from rat liver cytosol on enzyme activation by Ca²⁺ was investigated. Pyruvate kinase (adenosine triphosphate : pyruvate 2-Ο- phosphotransferase; EC 2.7.1.40) isolated from liver cytosol was activated by addition of Ca²⁺ in the range of 1.0-10³ μm; the concentration giving a half-maximal effect was 10 μm Ca²⁺. The enzyme activation by 10 μm Ca²⁺ addition was reversed by the presence of CaBP (4-40 μg/ml). With increasing concentrations of Ca²⁺ (1, 10 and 100, um Ca²⁺), the pyruvate kinase activity increased progressively. The increase of the enzyme activity by Ca²⁺ was clearly prevented by the presence of CaBP (20 μ/ml). CaBP had no effect on pyruvate kinase activity in the absence of Ca²⁺. Meanwhile, calmodulin (2.5-10 μg/ml) also reversed the activation of pyruvate kinase by Ca²⁺ (1 and 10 μM). These results indicate that CaBP may regulate the activation of pyruvate kinase by Ca²⁺. In particular, a novel CaBP may play an important role in the regulation of the Ca²⁺ effect on pyruvate kinase.