Transglutaminase-catalysed cross-linking of proteins phosphorylated in the intact glucose-stimulated pancreatic beta-cell.
Incubation of intact islets in the presence of [32P]Pi and stimulatory levels of glucose followed by separation of phosphorylated islet proteins by SDS-polyacrylamide gel electrophoresis revealed the presence of a high molecular weight phosphopolymer which did not transverse a 3% (w/v) acrylamide gel. The majority of this phosphopolymer (approx. 70%) was present in the 600 x g sedimented fraction of islet homogenates. Islet homogenates obtained from intact islets previously incubated with [32P]Pi and stimulatory levels of glucose when incubated under conditions that activated the islet transglutaminase resulted in an increase in the amount of phosphopolymer present in the 600 x g sedimented fraction. Inhibitors of transglutaminase activity which are known to inhibit glucose-stimulated insulin release led to a significant reduction in the fraction of phosphopolymer present in the glucose-stimulated intact islet. These findings suggest that protein cross-linking and phosphorylation reactions may be closely linked in the pancreatic beta-cell.
D000818:Animals; D001704:Biopolymers / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005947:Glucose / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008970:Molecular Weight; D009924:Organ Culture Techniques; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D051381:Rats; D011919:Rats, Inbred Strains; D011503:Transglutaminases / Q000378:metabolism*
D001704:Biopolymers; D010750:Phosphoproteins; D011503:Transglutaminases; D005947:Glucose