Eflfect of Sulfhydryl-Binding Reagents on Insulin Release from Isolated Secretion Granules¹

Abstract

The effect of various sulfhydryl-binding reagents on the release of insulin from secretion granules has been studied. Secretion granules isolated from toadfish islet tissue by differential centrifugation in sucrose were incubated in the test mtjdium, the granules were centrifuged down, and the medium was assayed for insulin using the epididymal fat pad method. When the granules were suspended in saline, about 20% of the total insulin in the granules was released into the medium. Monothiol-binding reagents (p-hydroxymercuribenzoate, phenylmercuric nitrate, and diphenylchloroarsine) at concentrations between 10−3 and 10−6M produced a 2- to 4-fold increase in insulin release. In contrast, dithiol-binding reagents (Cd††, Co++, Hg++) decreased the amount of insulin released into the medium and N-ethylmaleimide, iodoacetic acid, arsenite, dichlorophenylarsine, and amino group-binding reagents (trinitrobenzene sulfonic acid and 2-methoxy-5-nitrotropone) had neither effect. These results indicate that sulfhydryl ...