Isolation and characterization of multiple molecular forms of cytosolic NAD-linked glycerol-3-phosphate dehydrogenase from normal and neoplastic rabbit tissues.

Forms of cytosolic NAD-linked glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) have been isolated to homogeneity in yields as high as 70% from rabbit muscle, liver, mammary gland, and heart, and partially purified from rabbit Brown Pearce carcinoma. The purified enzyme forms have been characterized by flat plate isoelectric focusing, heat inactivation, comparative kinetics, antibody inactivation studies, and amino acid analysis. The enzyme activity in white skeletal muscle, mammary gland, and liver is composed predominantly of a form which focuses at pH 6.5 while the major form from heart focuses at pH 6.1. The major form from muscle, liver, and mammary gland is indistinguishable by all the techniques applied, The heart form of the enzyme is distinct from the major enzyme form in muscle, liver, and mammary gland by flat plate isoelectric focusing, heat inactivation, amino acid analysis, comparative kinetics, and antibody inactivation studies, but has the same subunit molecular weight. Two closely spaced minor forms have been isolated from liver that focus between the heart and muscle enzyme forms (pH 6.3). The apparent K,,, values of these forms indicate that they are not hybrids of the heart and muscle isoenzymes. Rabbit Brown Pearce carcinoma glycerol-3-phosphate dehydrogenase has been purified by affinity chromatography and appears on flat plate isoelectric focusing as an anionic form distinct from any previously found in normal rabbit tissues.