de Gunzburg J, Hohman R, Part D, Veron M
Biochimie. 1983 Jan;65(1):33-41. doi: 10.1016/s0300-9084(83)80026-1.
A cAMP-adenosine binding protein partially purified from exponentially growing Dictyostelium discoideum cells carries S-adenosyl-L-homocysteine (SAH) hydrolase activity. This protein is present throughout the developmental cycle and has many properties in common with a cAMP binding activity previously reported from this laboratory (Gunzburg and Véron, 1981). Direct binding measurements with radioactive ligands indicate a dissociation constant of 0.2 microM for adenosine and 9 nM for cAMP, a value in good agreement with measurements of the rate constants for cAMP binding (k+1 = 2.4 X 10(4) M-1 sec-1) and dissociation (k-1 = 1.1 X 10(-4) sec-1). The binding of cAMP is completely abolished in the presence of 1 microM adenosine; a maximum 60 per cent inhibition of adenosine binding can be achieved with cAMP concentrations as high as 0.1 microM, suggesting that at least some of the cAMP and adenosine binding sites are not identical. The protein has a sedimentation coefficient of 9.2S and a native molecular weight of 190,000, as judged by gel filtration. Labeling with the photoaffinity ligand 8-azido-[3H]-cAMP followed by SDS polyacrylamide gel electrophoresis results in a single band of 47,000 MW, suggesting that the protein may be a tetramer. The physiological importance of the protein and its association with SAH hydrolase activity is discussed in relation to a possible role in the regulation of protein and phospholipid methylation that occurs during chemotaxis.
从指数生长期的盘基网柄菌细胞中部分纯化得到的一种环磷酸腺苷 - 腺苷结合蛋白具有S - 腺苷 - L - 高半胱氨酸（SAH）水解酶活性。该蛋白在整个发育周期中都存在，并且具有许多与本实验室先前报道的环磷酸腺苷结合活性相同的特性（贡茨堡和韦龙，1981年）。用放射性配体进行的直接结合测量表明，腺苷的解离常数为0.2微摩尔，环磷酸腺苷的解离常数为9纳摩尔，该值与环磷酸腺苷结合速率常数（k + 1 = 2.4×10⁴ M⁻¹秒⁻¹）和解离速率常数（k - 1 = 1.1×10⁻⁴秒⁻¹）的测量结果高度一致。在存在1微摩尔腺苷的情况下，环磷酸腺苷的结合完全被消除；当环磷酸腺苷浓度高达0.1微摩尔时，腺苷结合的最大抑制率可达60%，这表明至少一些环磷酸腺苷和腺苷结合位点并不相同。通过凝胶过滤判断，该蛋白的沉降系数为9.2S，天然分子量为190,000。用光亲和配体8 - 叠氮基 - [³H] - 环磷酸腺苷标记，然后进行十二烷基硫酸钠聚丙烯酰胺凝胶电泳，结果显示出一条分子量为47,000的单带，这表明该蛋白可能是一种四聚体。本文讨论了该蛋白的生理重要性及其与SAH水解酶活性的关联，涉及到它在趋化作用过程中蛋白质和磷脂甲基化调节中可能发挥的作用。
