Thiol-protein disulphide oxidoreductases. Differences between protein disulphide-isomerase and glutathione-insulin transhydrogenase activities in ox liver.
1. Protein disulphide-isomerase and glutathione-insulin transhydrogenase activities were assayed in parallel through a conventional purification of protein disulphide-isomerase from ox liver. 2. Throughout a series of purification steps (differential centrifugation, acetone extraction, (NH4)2SO4 precipitation and ion-exchange chromatography), the two activities appeared in the same fractions but were purified to different extents. 3. The final sample was 143-fold purified in protein disulphide-isomerase but only 10-fold purified in glutathione-insulin transhydrogenase; nevertheless the two activities in this preparation were not resolved by high-resolution isoelectric focusing and both showed pI4.65. 4. In a partially purified preparation containing both activities, glutathione-insulin transhydrogenase was far more sensitive to heat denaturation than was protein disulphide-isomerase; conversely protein disulphide-isomerase was more sensitive to inactivation by deoxycholate. 5. The data are inconsistent with a single enzyme being responsible for all the protein disulphide-isomerase and glutathione-insulin transhydrogenase activity of ox liver. It is suggested that several similiar thiol-protein disulphide oxidoreductases of overlapping specificities may better account for the data.
D000818:Animals; D002417:Cattle; D003840:Deoxycholic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D007525:Isoelectric Focusing; D007535:Isomerases / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D010088:Oxidoreductases / Q000378:metabolism*; D011490:Protein Disulfide Reductase (Glutathione) / Q000302:isolation & purification / Q000378:metabolism*
D003840:Deoxycholic Acid; D010088:Oxidoreductases; D011490:Protein Disulfide Reductase (Glutathione); D007535:Isomerases