Couplage de la corticotropine‐β1–24 avec le système adénylate cyclase des adipocytes de rat

摘要: The Coupling of β1-24-Corticotropin to the Adenylate-Cyclase System in Rat Adipocytes. Evidence for Hormone-Nucleotides Interaction The general aim was define some most important parameters involved coupling step between synthetic analog adrenocorticotropin hormone (β1−24-corticotropin tetracosa peptide) and catalytic unit adenylate-cyclase system fat cells. These studies were performed with a purified plasma membrane fraction from rat adipose tissue. In this regard, effects ions, pH, nucleotides (ATP GTP) on hormone-sensitive studied. A simple model based random association process reactants yielded satisfactory approximation kinetic data. In contrast results obtained by two other groups, which analyzed De Haen [J. Biol. Chem. (1974) 249, 2756–2762], no evidence found regulation activity adenosine triphosphate not complexed magnesium. inhibition observed an excess substrate, ATP-magnesium complex, independent concentration Mg2+ free ATP4−. Increasing pH incubation medium 7.0 9.6 resulted sigmoidalcurve basal β1−24-corticotropin-stimulated without affecting response hormone. contrast, activity, presence fluoride ion, showed optimum at 8.0 then dramatically decreased higher values. This observation suggested dissociation stimulation processes. The addition 1 mM ethylene glycol bis (β-aminoethylether)-N,N′-tetracetic acid mixture led adenylate cyclase s1−24-corticotropin. While activation ratio (the stimulated levels) unchanged range 0.05 – 5 Ca2+, hormonal progressively inhibited 0.1 La3+ disappeared completely La3+. From these data it apparent that Ca2+ antagonist, competed critical sites binding required β1−24-corticotropin cyclase. In substrate gave good correlation Michaelis-Menten kinetics (0.006–0.3 ATP) we calculated Km values substrate; they 2 × 10−5 M basal, 2.5 ion-stimulated 4 6 β1-24-corticotropin-stimulated activity. activators increased essentially its V. The measurement β1−24-corticotropin-sensitive as function ATP maximum value. plot due versus simulated rate equations derived reaction scheme presented; curve experimental closely approximated theoretical curve. Therefore, concluded stimulatory effect did require hypothetical regulatory site nucleotide. A thermodependent guanosine fat-cell β1−24-corticotropin. Moreover, 37 °C, GTP observed; dependent. At low concentrations, enhanced both hormone-stimulated resulting ratio.