Activation of glucose uptake by insulin and insulin-like growth factor I in Xenopus oocytes.
Xenopus laevis oocytes possess a glucose transport system that is activated 3- to 5-fold by insulin-like growth factor I (Ka = 3 nM) and insulin (Ka = 200-250 nM), properties suggesting activation mediated by an insulin-like growth factor I receptor. This activation increases the Vmax of hexose uptake and has little or no effect on the Km for deoxyglucose (Km = 1-2 mM). Activation by hormone requires about 60 min and is inhibited by cytochalasin B but not by cycloheximide. The dependence of hexose uptake rate on hexose concentration exhibits cooperativity with Hill coefficients of 1.8 and 1.4 for the basal and hormone-activated states, respectively. Microinjection of a monoclonal antibody directed against the tyrosine kinase domain of the human insulin receptor blocks activation of hexose uptake by insulin-like growth factor I and insulin but has no effect on basal uptake. Taken together the results implicate the tyrosine-specific protein kinase activity of a cell-surface insulin-like growth factor I receptor in the activation of glucose transport in the Xenopus oocyte.
Janicot
M
M
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Lane
M D
MD
D000818:Animals; D001692:Biological Transport; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism*; D006601:Hexoses / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009865:Oocytes; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D013002:Somatomedins / Q000494:pharmacology*; D014982:Xenopus laevis / Q000502:physiology*
D006601:Hexoses; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D005947:Glucose