The nature of human serum insulin-like activity (ILA): characterization of ILA in serum and serum fractions obtained by acid-ethanol extraction and adsorption chromatography

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Abstract
Studies were undertaken in an attempt to clarify the apparent heterogeneous nature of human serum insulin-like activity. Methods of preparative zone electrophoresis on Pevikon, acid-ethanol extraction of trichloroacetic acid serum protein precipitates, adsorption chromatography on DEAE-cellulose and Dowex 50, gel filtration chromatography, and insulin antiserum immunoreactivity were used. The results establish the presence of a substance in serum with in vitro biological properties similar to insuln but with different physicochemical properties. The major portion of serum ILA measured by bioassay techniques can be attributed to the effects of this substance. Whereas the in vitro biological effects of this substance on muscle and adipose cells were similar to those of crystalline insulin, the substance is distinguished from insulin by: (1) the failure of insulin antiserum to inhibit its in vitro biological effect; (2) a slower electrophoretic mobility (in the gamma-beta globulin zone); and (3) a larger molecular weight, between 40,000 and 50,000 in these studies. It is similar to insulin since both are soluble in acid-ethanol. The results further indicate that previously described insulin-like activity in gamma-beta globulin preparations, the major portion of total serum insulin activity described in acid-ethanol extracts of serum, “bound” insulin, “atypical” insulin, and antibody nonsuppressible insulin-like activity bioassayed in diluted serum are all one and the same substance.