Sugden M C, Ashcroft S J
Biochem J. 1981 Aug 1;197(2):459-64. doi: 10.1042/bj1970459.
Cyclic nucleotide phosphodiesterase activity towards cyclic AMP and cyclic GMP was studied in extracts of rat islets of Langerhans. Biphasic Eadie plots [Eadie (1942) J. Biol. Chem. 146, 85-93] were obtained with either substrate suggesting the presence of both 'high'- and 'low'-Km components. The apparent Km values were 6.2 +/- 0.5 (n = 8) microM and 103.4 +/- 13.5 (6) microM for cyclic AMP and 3.6 +/- 0.3 (12) microM and 61.4 +/- 7.5 (13) microM for cyclic GMP. With cyclic AMP as substrate, phosphodeisterase activity was increased by calmodulin and Ca2+ and decreased by trifluoperazine, a specific inhibitor of calmodulin. With cyclic GMP as substrate, phosphodiesterase activity was decreased by omission of Ca2+ or addition of trifluoperazine. Addition of exogenous calmodulin had no effect on activity. The data suggest that Ca2+ may influence the islet content of cyclic AMP and cyclic GMP via effects on calmodulin-dependent cyclic nucleotide phosphodiesterase(s).
对大鼠胰岛提取物中针对环磷酸腺苷（cAMP）和环磷酸鸟苷（cGMP）的环核苷酸磷酸二酯酶活性进行了研究。使用任何一种底物均得到双相伊迪曲线[伊迪（1942年）《生物化学杂志》146卷，85 - 93页]，这表明存在“高”和“低”Km组分。cAMP的表观Km值分别为6.2±0.5（n = 8）微摩尔和103.4±13.5（6）微摩尔，cGMP的表观Km值分别为3.6±0.3（12）微摩尔和61.4±7.5（13）微摩尔。以cAMP为底物时，磷酸二酯酶活性被钙调蛋白和Ca²⁺增强，被钙调蛋白的特异性抑制剂三氟拉嗪降低。以cGMP为底物时，通过去除Ca²⁺或添加三氟拉嗪可降低磷酸二酯酶活性。添加外源性钙调蛋白对活性无影响。数据表明，Ca²⁺可能通过影响钙调蛋白依赖性环核苷酸磷酸二酯酶来影响胰岛中cAMP和cGMP的含量。
