[Purification and some properties of molecular forms of 6-phosphogluconate dehydrogenase from rat liver].

Using stepwise protein fractionation by (NH4)2SO4 and ion-exchange chromatography on CM-cellulose, DEAE-cellulose and SP-Sephadex, two isoforms of 6-phosphogluconate dehydrogenase, A and B, from rat liver were obtained. The method developed allows to achieve complete separation of these forms and to obtain preparative amounts of the protein with specific activities of 5.7 and 10.7, respectively. The native enzyme forms A and B have molecular weights of 107000 and are represented by dimers composed of subunits with identical molecular weights equal to 54000. Both isoforms have a pH optimum at 8.5 and reveal different sensitivity to MgCl2 and MnCl2. The tetrahedron-shaped ions (phosphate, molibdate, arsenate) inhibit the both molecular forms of the enzyme, The Arrhenius plots for the reaction rate are uninterrupted lines within the temperature range of 21-44 degrees; the values of activation energy and the temperature coefficient for isoforms A and B are 12750 and 13500 cal/mole and 2.05 and 2.15, respectively.