title: Decreased biologic activity and degradation of human [SerB24]-insulin, a second mutant insulin.
abstract: A second mutant insulin, identified as [SerB24]-insulin, has a highly hydrophilic character. To determine the biologic activity and the degradation of this mutant insulin, human [SerB24]- and [SerB25]-insulin analogues were semisynthesized from porcine insulin by an enzyme-assisted coupling method. All of the following studies on isolated rat adipocytes were performed at 37 degrees C to directly correlate the binding potency and the biologic activity. The ability of these insulins to displace 125I-porcine insulin bound to adipocytes was 0.5-2% and 1-4%, respectively, of porcine insulin. When the ability of these insulins to stimulate glucose transport and glucose oxidation was measured, both analogues had full activity at high concentrations (250 ng/ml). However, ED50 of the porcine, [SerB24]-, and [SerB25]-insulins to stimulate glucose transport was 0.37 +/- 0.05, 46.3 +/- 5.4, and 23.3 +/- 5.5 ng/ml, respectively. Similarly, for glucose oxidation, ED50 was 0.38 +/- 0.06, 33.8 +/- 3.6, and 16.6 +/- 3.4 ng/ml, respectively. Thus, the biologic activity of [SerB24]- and [SerB25]-insulins was reduced to 0.5-2% and 1-4% of that of porcine insulin, which was compatible with our previous studies under different conditions. No antagonistic effects were observed for either analogue. Degradation of 125I-labeled [SerB24]- and [SerB25]-insulins was also decreased to 62.8% and 55.8%, respectively, of 125I-porcine insulin. These results confirm the importance of the hydrophobic residues at B24 and B25 in the biologic activity of insulin; the patient having this hydrophilic insulin was considered to be in an insulinopenic state despite the hyperinsulinemia due to decreased degradation of the mutant insulin.
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002851:Chromatography, High Pressure Liquid; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000031:analogs & derivatives* / Q000235:genetics* / Q000378:metabolism; D008297:Male; D009154:Mutation; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism; D013552:Swine
chemical_list: D007328:Insulin; C040795:insulin, Ser(B25)-; C031724:insulin, Leu(B24)-; C040796:insulin, Ser(B24)-; D011972:Receptor, Insulin; D005947:Glucose