Scarpace P J, O'Connor S W, Abrass I B
Life Sci. 1983 Feb 21;32(8):817-24. doi: 10.1016/0024-3205(83)90217-5.
The thermal inactivation of adenylate cyclase was investigated in human lymphocytes and in the N-protein deficient cyc- S49 mouse lymphoma cell line. The enzyme is rapidly inactivated at 37C with a t1/2 of 5.5 and 4.5 min respectively in human and cyc- membranes. Thermal inactivation is prevented by at least two mechanisms. The first mechanism involves ATP which stabilizes adenylate cyclase in a concentration dependent manner similar to the Km of ATP for cAMP formation. However, the inhibition of inactivation does not require Mg++ while the enzyme catalysis of ATP to cAMP does. The second mechanism involves substances which activate the enzyme. The human lymphocyte enzyme is equally stabilized by either NaF, GppNHp, or forskolin. In contrast, the cyc- enzyme is fully stabilized by forskolin but only partially stabilized by NaF. When human erythrocyte N-protein extract is added to cyc- membranes, NaF fully stabilizes the enzyme. These data suggest that an activated N-protein is instrumental in stabilizing adenylate cyclase and that there is some N-protein component in cyc- membranes through which NaF may be exerting its stabilizing action.
在人淋巴细胞和缺乏N蛋白的cyc-S49小鼠淋巴瘤细胞系中研究了腺苷酸环化酶的热失活情况。在37℃时，该酶在人细胞膜和cyc-细胞膜中分别以5.5分钟和4.5分钟的半衰期迅速失活。热失活至少通过两种机制来防止。第一种机制涉及ATP，它以浓度依赖的方式稳定腺苷酸环化酶，类似于ATP对cAMP形成的Km值。然而，失活的抑制不需要Mg++，而ATP催化生成cAMP的酶促反应需要Mg++。第二种机制涉及激活该酶的物质。人淋巴细胞中的酶可被NaF、GppNHp或福斯可林同等程度地稳定。相比之下，cyc-酶可被福斯可林完全稳定，但仅被NaF部分稳定。当将人红细胞N蛋白提取物添加到cyc-细胞膜中时，NaF可完全稳定该酶。这些数据表明，活化的N蛋白有助于稳定腺苷酸环化酶，并且cyc-细胞膜中存在一些N蛋白成分，NaF可能通过这些成分发挥其稳定作用。
