Rat pancreatic islet homogenates catalyze the incorporation of [2,5−3-H]histamine into endogenous proteins recovered in both the stacking gel and a Mr 84000 protein separated by polyacrylamide electrophoresis. The labelling of these proteins represents a Ca2+-dependent process inhibited by glycine methylester, but not sarcosine methylester, and enhanced after preincubation of the islets at a high concentration of D-glucose. Although transglutaminase activity is found in both soluble and particlate subcelluler fractions, the endogenous transglutaminase substrates were located mainly in paarticulate, possibly membrane-associated, material.

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