Abstract
It is not yet known whether insulin exerts its various metabolic effects only through interaction with cell surface, or by acting at a specific site within the cell.
The present study was designed to explore the reaction mechanism of insulin by using synthetic dextran-insulin complex which is soluble and poorly permeable to cell membrane.
Crystalline bovine insulin was covalently coupled at pH 9 with dextran (MW=40,000 or 70,000) which had been activated with CNBr by slight modification of procedure described by Axen and Porath. After coupling, dextran-insulin was precipitated with acetone and purified by gel filtration through a column of Sephadex G-75. Bound insulin in dextran-insulin complex was determined by a micromethod using polyacrylamide gel electrophoresis. The shape of radioimmunoassay curve of dextran-insulin indicated that its immunochemical effectiveness is lower than that of unmodified free insulin. Next, when dextran-insulin was injected intravenously into alloxan-diabetic rats, the blood glucose concentration extensively lowered at a dose as little as 0.4U/kg. Its hypoglycemic action was not only potent, but also long acting, compared with unmodified insulin. It was also found that dextran-insulin markedly induced glucokinase, pyruvate kinase, and ATP citrate lyase in the liver at a much smaller amount than that of free insulin, after injection into alloxandiabetic rats.
