Multiple molecular forms of cytoplsmic glycerol-3-phosphate dehydrogenase in rat liver

Two major zones of cytoplasmic l-glycerol-3-P dehydrogenase (EC 1.1.1.8) activity appeared in polyacrylamide gel isoelectric focusing analysis of homogenates of livers from rats weighing 300-350 g. At least three other minor zones of activity were also observed. The more anionic of the two major zones of activity does not appear in homogenates of livers from smaller rats but can be generated in vitro by storing the homogenates overnight at 4°. Liver homogenates could be resolved into three zones of activity by DEAE-Sephadex column chromatography. Two of these isoenzymic forms of the enzyme were isolated at a high level of purity by a series of steps including a final column of DEAE-Sephadex and were characterized by amino acid analysis. One of these two forms was indistinguishable from the single major form of the enzyme isolated and characterized from livers of smaller rats and corresponded to the more cationic of the two major forms of the enzyme observed by gel electrofocusing in this work. The second form isolated corresponded to the most cationic of the minor forms of the enzyme observed in gel electrofocusing. Alternative methods of smaple introduction into electrofocusing gels were employed including internal layering and injection, in addition to the usual polymerization of the sample throughout the gel.