Conversion of (125I)insulin and (125I)proinsulin into high molecular weight forms in vivo.

Abstract

Single component porcine [125I] insulin and bovine [125I]proinsulin injected in rats were converted into high molecular weights forms. These high molecular weight forms were reactive with guinea pig antisera against crystalline insulin although their immunoreactivity was diminished (65 to 75%) compared to that of control [125I]insulin and [125I]proinsulin (over 95%). Within 2 to 4 min of injection about 20% of the total immunoprecipitable radioactivity of rat sera appeared in the high molecular weight region (70,000 to 100,000 daltons) and within 2 hr it represented over 80%. A 4-hr incubation of control [125I]insulin and [125I]proinsu-lin with rat sera in vitro did not result in the production of high molecular weight forms. Denaturation with 8M urea-2% SDS did not affect significantly the high molecular weight forms of insulin or proinsulin. When denaturation was combined with sulfitolysis about 95% of the radioactivity of the high molecular weight [125I]insulin appeared in the A- and B-chain regions, suggesting the involvement of disulfide bonds in the formation of the high molecular weight forms of [125I]insulin. Under the same conditions of denaturation and sulfitolysis about 52% of the radioactivity of the high molecular weight [125I]proinsulin remained in the high molecular weight fraction. (Endocrinology95: 1543, 1974)