Phosphorylase phosphatase activities of rat liver in streptozotocin-diabetes.
Protein phosphatase-1 and 2A, accounting for all the hepatic activity regulating phosphorylase, were assayed in streptozotocin-induced (8 weeks) diabetic Wistar rats. Cytosolic protein phosphatase-1 and 2A were distinguished by chromatography on heparin-Sepharose and by inhibition with inhibitor-2. Approx. 25-35% increases in type-1 phosphorylase phosphatase activity measured in cytosols were registered in diabetic rats when compared with control and 24 h fasting animals. The enrichment of protein phosphatase-1 in the cytosol of streptozotocin-treated rat livers could not be attributed to the reduced glycogen content with the onset of diabetes, since this elevated level of type-1 phosphatase was not observed in fasting rats with low glycogen content. The translocation of type-1 phosphatase from the particulate fraction into the cytosol was also recorded in trypsin-treated samples of diabetic rat livers. The apparent molecular weight of type-1 phosphatase in the cytosol of control and fasted rats was 160,000 as judged by gel filtration. The type-1 phosphatase activity that was released from the particulate fraction by streptozotocin-induced diabetes identified a further enzyme species (Mr 110,000) in the cytosol. Our data imply that the higher levels of cytosolic protein phosphatase-1 in diabetic rat liver could be a consequence of the dissociation of the catalytic subunit of protein phosphatase-1 and the glycogen-binding subunit in rat livers.
Csortos
C
C
Department of Medical Chemistry, University School of Medicine, Debrecen, Hungary.
Farkas
I
I
Sparks
L
L
Bányász
T
T
Kovács
T
T
Gergely
P
P
D000818:Animals; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D005215:Fasting; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010765:Phosphorylase Phosphatase / Q000302:isolation & purification / Q000378:metabolism*; D054645:Protein Phosphatase 1; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013347:Subcellular Fractions / Q000201:enzymology
D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D010765:Phosphorylase Phosphatase