Salomon Y, Amir Y, Azulai R, Amsterdam A
Biochim Biophys Acta. 1978 Dec 1;544(2):262-72. doi: 10.1016/0304-4165(78)90095-8.
Heparin inhibits (I50 = 2 microgram/ml) the activity of luteinizing hormone and human chorionic gonadotropin-stimulated adenylate cyclase in purified rat ovarian plasma membranes. Unstimulated enzyme activity and activity stimulated by NaF, GTP or guanosine 5'-(beta,gamma-imido)triphosphate were inhibited to a lesser extent. Human chorionic gonadotropin binding to this membrane preparation was inhibited by heparin (I50 = 6 microgram/ml). The inhibition with respect to hormone concentration was of a mixed type for hormone binding and adenylate cyclase stimulation. Inhibition by heparin was not eliminated at saturating hormone concentration. The degree of inhibition was unaffected by the order in which enzyme, hormone and heparin were introduced into the assay system. Heparin (3 microgram/ml) did not affect the pH activity relationship of basal and hormone-stimulated adenylate cyclase activity and did not change the dependence of enzyme activity on magnesium ion concentration. The inhibitory action of heparin cannot be solely attributed to interference with either catalysis or hormone binding. The possibility is considered that the highly charged heparin molecule interferes with enzyme receptor coupling, by restricting the mobility of these components or by effecting their conformation.
肝素抑制（半数抑制浓度I50 = 2微克/毫升）纯化的大鼠卵巢质膜中促黄体生成素和人绒毛膜促性腺激素刺激的腺苷酸环化酶的活性。未受刺激的酶活性以及由氟化钠、鸟苷三磷酸或鸟苷5'-（β，γ-亚氨基）三磷酸刺激的活性受到的抑制程度较小。肝素抑制（半数抑制浓度I50 = 6微克/毫升）人绒毛膜促性腺激素与这种膜制剂的结合。对于激素结合和腺苷酸环化酶刺激，相对于激素浓度的抑制是混合型的。在饱和激素浓度下，肝素的抑制作用并未消除。抑制程度不受将酶、激素和肝素引入测定系统的顺序的影响。肝素（3微克/毫升）不影响基础和激素刺激的腺苷酸环化酶活性的pH活性关系，也不改变酶活性对镁离子浓度的依赖性。肝素的抑制作用不能仅仅归因于对催化或激素结合的干扰。有人认为，高度带电的肝素分子通过限制这些成分的流动性或影响其构象来干扰酶受体偶联。
