Crooke M J, Sneyd J G
Biochim Biophys Acta. 1980 Aug 1;631(1):40-8. doi: 10.1016/0304-4165(80)90051-3.
Isolated hepatocytes converted exogenous [alpha-32P]ATP to cyclic [32P]AMP at high rates. This system was used for kinetic studies of the effects of glucagon, fluoride, free magnesium and free ATP4- on adenylate cyclase. In the absence or presence of glucagon, free Mg2+ activated adenylate cyclase by decreasing the Km for MgATP2- without changing V. Free ATP4- was not a potent inhibitor of adenylate cyclase and the only effect of glucagon was to increase V. Fluoride also increased the V of adenylate cyclase, but, in contrast to the results obtained with glucagon, the effect increased as the concentration of free Mg2+ increased. One explanation of the effect of fluoride, consistent with the idea that free Mg2+ activates adenylate cyclase and free ATP is not an inhibitor, is that fluoride increases the affinity of the enzyme for Mg2+. Weak inhibition of adenylate cyclase by ATP4- in the presence of fluoride cannot be excluded.
分离的肝细胞能将外源性[α-32P]ATP高效地转化为环[32P]AMP。该系统用于对胰高血糖素、氟化物、游离镁和游离ATP4-对腺苷酸环化酶作用的动力学研究。在不存在或存在胰高血糖素的情况下，游离Mg2+通过降低MgATP2-的Km而不改变V来激活腺苷酸环化酶。游离ATP4-不是腺苷酸环化酶的有效抑制剂，胰高血糖素的唯一作用是增加V。氟化物也增加腺苷酸环化酶的V，但与胰高血糖素的结果相反，随着游离Mg2+浓度的增加，其作用增强。与游离Mg2+激活腺苷酸环化酶且游离ATP不是抑制剂这一观点一致的对氟化物作用的一种解释是，氟化物增加了酶对Mg2+的亲和力。在氟化物存在下，不能排除ATP4-对腺苷酸环化酶的微弱抑制作用。
