Insulin-like substance and insulin-degrading complex of hemolysate of human erythrocytes

A lysate of human erythrocytes was fractionated on gel-filtration resins of different types and immunoreactive insulin, the insulinase activity and the effect of individual fractions on the insulinase activity was determined in the fractions obtained. It was established that the hemolysate contains a complex of insulin-metabolizing compounds, including an insulin-like substance, insulinase, and an inhibitor and activator of the insulinase activity. The insulin-like substance coincided with native insulin in site of elution from a column of Sephadex G-50 and its concentration in the lysate exceeded that of insulin in the blood plasma. Insulinase, which has a molecular weight of about 100,000, cleaved [125I] insulin to fragments soluble in trichloroacetic acid, but had no effect on hypophyseal proteins and glycoprotein hormones. The insulinase activity was inhibited by low temperatures, atropine, and a newly discovered intraerythrocytic proteinase inhibitor, which also inhibits the serine proteinases trypsin and chymotrypsin. A substance eluted from a column of Sephadex G-100 in the region of low-molecular-weight substances increased the insulinase activity. The elution curve of substances with proteinase-inhibiting and insulinase-activating activities indicates that there is more than one inhibitory and activating factor. The results of the studies suggest that the insulin-degrading complex in human erythrocytes acts as a regulator of the insulin level in the blood plasma. It is also possible that the insulin-like substance is produced in the cytosol of the erythrocytes