THE EFFECT OF LIPID MICELLES ON MITOCHONDRIAL MALATE DEHYDROGENASE

Abstract

Mitochondrial malate dehydrogenase (M-MDH) is known to be very unstable in aqueous solution. This instability may be ascribed to removal of the enzyme by severe extraction procedures from its bound state in the mitochondrion.Whole heart lipid micelles, mitochondrial lipids, and fatty acids increase the stability of the enzyme. The degree of lipid ability to increase activity of M-MDH is dependent on the ionic character of the environment. Thus the enzyme exhibits higher activity in a lipid–phosphate system than in lipid–Tris–acetate or lipid–KCl. Likewise, the enzymatic activity is higher in lipid than in non-lipid media. The relative ability of lipid to stimulate M-MDH activity is independent of pH, ionic strength, and temperature (between 6 and 37 °C). Preliminary evidence suggests that lipid acts by altering the conformation of the tertiary structure of the enzyme.The results, in general, suggest that hydrophobic-group interactions increase enzyme stability. These interactions may, in part, simulate the actual type of binding which stabilizes the enzyme activity in vivo.