concanavalin-a and vitamin-k5

An insulin-stimulating peptide derived from bovine serum albumin by digestion with trypsin was shown to inhibit insulin degradation. Addition of this peptide (1.2 microM) to the medium of isolated rat adipocytes markedly inhibited the degradation of insulin in the medium, but had a little effect on degradation of cell-associated insulin. Moreover, this peptide did not prevent dissociation of cell-associated insulin, suggesting that it is a bacitracin-type, not a chloroquine-type inhibitor of insulin degradation. The peptide also potentiated the stimulation by insulin mimickers of glucose oxidation by rat adipocytes, strongly indicating that it has some other effects besides inhibition of insulin degradation. Therefore, the effect of the peptide on activation of pyruvate dehydrogenase (PDH), one of the postbinding actions of insulin, was studied. Addition of the peptide (4 microM) to adipocytes was found to activate PDH in the absence or presence of insulin. This stimulatory effect of the peptide on PDH was dose-dependent and was observed in both whole cells and subcellular fractions of rat adipocytes. The peptide also stimulated PDH in a subcellular system of either plasma membranes and mitochondria or mitochondria only. Sodium fluoride, an inhibitor of phosphatase, blocked the action of the peptide almost completely, suggesting that the stimulatory effect of the peptide on PDH activity is at least partly due to its activation of PDH phosphatase. The mechanisms of action of the peptide are discussed. The peptide should be useful in studies on modulation of the action of insulin.

Topics: Adipose Tissue; Animals; Cell Membrane; Chloroquine; Concanavalin A; Drug Synergism; Glucose; Insulin; Intercellular Signaling Peptides and Proteins; Male; Mitochondria; Oxidation-Reduction; Peptides; Pyruvate Dehydrogenase Complex; Rats; Rats, Inbred Strains; Serum Albumin, Bovine; Vitamin K; Vitamin K 3; Wheat Germ Agglutinins

The effects of insulin and several insulin-mimetic agents on rat adipocyte D-glucose metabolism were studied in an effort to determine if any of the insulin-mimetic agents could be used to define the mechanism of insulin action. Antibodies against rat adipocyte plasma membranes have been characterized as having insulin-mimetic effects on glucose transport and these effects may be caused by divalent clustering of cell surface antigens. In contrast to insulin, antimembrane antibodies had little stimulatory effect on D-glucose conversion to lipids in isolated rat adipocytes, under conditions where both reagents stimulated D-glucose oxidation. Among other insulin-mimetic agents tested, the reagents hydrogen peroxide and concanavalin A most closely resembled insulin in their ability to increase both [14C]-CO2 and [14C]-lipid formation from [14C]D-glucose in rat adipocytes. Vitamin K5 and diamide had the unusual effect of inhibiting [1-14C]D-glucose conversion to [14C]-lipids at a concentration that gave maximal stimulation of glucose oxidation by rat adipocytes. Analysis of the lipid components into which glucose derivatives were incorporated revealed that insulin increased D-glucose incorporation into both nonesterified fatty acids and triglycerides and H2O2 and concanavalin A had similar effects. These findings argue against the possibility that insulin and the antimembrane antibodies or the insulin-mimetic agents other than H2O2 and concanavalin A share the same mechanism of action.

Topics: Adipose Tissue; Animals; Antibodies; Cell Membrane; Chromatography, Thin Layer; Concanavalin A; Diamide; Female; Glucose; Hydrogen Peroxide; Insulin; Lipids; Oxidation-Reduction; Rats; Rats, Inbred Strains; Spermine; Vitamin K; Vitamin K 3