HIGH-RESOLUTION 2-DIMENSIONAL POLYACRYLAMIDE-GEL ELECTROPHORESIS REVEALS A GLUCOSE-RESPONSE PROTEIN OF 65-KDA IN PANCREATIC-ISLET CELLS

High-resolution two-dimensional PAGE was used to search for glucose-response proteins in isolated pancreatic islets that were labeled with [35S]methionine at ambient glucose concentrations of 0-18 mM. A 65-kDa protein, iso-electric focusing point of approximately 6.6-7.0, was discovered that showed at least a 20-fold stimulation of radiolabeling when glucose in the labeling medium was increased from 3 to 18 mM, in contrast to a 2.5-fold enhancement of label incorporation into total islet proteins. This 65-kDa protein is evident after 30 min of labeling with 18 mM glucose and is preferentially synthesized compared to its nearest neighbors after both 30 and 60 min of labeling. Glucose induction of the 65-kDa protein was virtually blocked by D-mannoheptulose. Glucose induction of this 65-kDa protein is in practically all aspects comparable to glucose induction of insulin and glucokinase in pancreatic β cells. A working hypothesis is developed proposing that glucose-response proteins or 'glucospondins' are pivotal constituents of pancreatic islet cells and that their discovery and exploration promise new insights into normal and pathological islet cell function.