THE INSULIN ACTIVITY OF PROTEIN FRACTIONS OF NORMAL HUMAN SERUM

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Abstract
SUMMARY: Protein fractions of normal human serum have been prepared by zone electrophoresis and their effect on the uptake of glucose by isolated rat diaphragm investigated. The uptake of glucose by isolated diaphragm is increased by the slower moving portion of the albumin peak, but not by the more rapidly moving part; from this it is concluded that serum albumin itself does not stimulate glucose uptake. Some stimulation of glucose uptake was also found with the β- and γ-globulin fractions. Since added ox insulin (131I-labelled or unlabelled) appears to migrate in the region of the slower moving portion of the albumin fraction it is suggested that the stimulating effect of this portion of the albumin fraction is due to circulating insulin. The stimulating effect of serum albumin prepared by fractional precipitation also appears to be due to insulin.