Human mitochondrial glycerol phosphate dehydrogenase (GPDm) isozymes

1. A hydrophobic/phospholipid electrophoretic system has been devised which makes possible the analysis of human mitochondrial glycerol phosphate dehydrogenase (E.C. 1.1.99.5. GPDM). 2. GPDM has a wide tissue distribution in both adult and foetal life and is active in cultured lymphoblastoid cells and fibroblasts but is absent from red cells. 3. The solubilization procedure does not significantly alter the kinetic properties of the enzyme (Km alpha-glycerophosphate = 0.04-0.07 M, Km PMS = 0.19-0.35 mM) but the soluble form is less thermostable. 4. Comparisons of physicochemical characteristics, tissue distribution and coenzyme requirement point to a separate genetic determination and low level of evolutionary relatedness between GPDM and its cytosolic counterpart GPDS.