THE ASSAY OF INSULIN IN VITRO BY FIBRIL FORMATION AND PRECIPITATION

An assay of insulin by fibril formation from small samples of pancreas

“…Contrary to Waugh et al (1950) andFoster et al (1951), who found pig fibrils to be the most efficient seed for recovery of insulin, no consistent species difference was observed. It may be suggested that the long period of rapid stirring used in the present procedure carried the fibril formation to completion so that individual differences in rate were unobservable.…”

“…The observation that the use of sulphuric acid in the original fibril method described by Waugh (1946) caused considerable precipitation of foreign protein could explain the lack of specificity reported by Foster et al (1951) andSutherland et al (1949). Most of this interference was prevented by using hydrochloric acid and rapid stirring.…”

“…A preparation of these insoluble fibrils would act as a seed in crude dilute solutions of insulin, and when this was carried out at the right pH the insulin was quantitatively precipitated. This method of assay has been criticized by Foster, MacDonald & Smart (1951) and by Light & Simpson (1956), who have reported that recoveries may be erratic in the presence of a crude mixture of tissue proteins. There is, indeed, evidence that globin (Foster et al 1951), muscle protein, serum albumin and fibrin (Waugh, Wilhelmson, Commerford & Sackler, 1953) can form insoluble aggregates under the prescribed conditions, and Sutherland, Cori, Haynes & Olsen (1949) found that glucagon could be precipitated as part of the fibril mat.…”