Davis C W, Daly J W
J Biol Chem. 1978 Dec 25;253(24):8683-6.
A calcium-dependent cyclic nucleotide phosphodiesterase from rat cerebrum was, in the absence of activator protein, inhibited by various monovalent cations. The inhibition was rapid, readily reversible, and concentration-dependent, with 100 mM cesium, rubidium, or potassium ion inhibiting essentially all basal enzyme activity, while 100 mM sodium or lithium ions produced only moderate inhibition. The potency of the cations in inhibiting the enzyme was Cs greater than or equal to Rb greater than K greater than Na greater than or equal to Li. Potassium ions increased the apparent Km for cyclic GMP and cyclic AMP by 3- and 5-fold, respectively. At 100 mM, the monovalent cations inhibited enzyme activated by the calcium-dependent activator by only 15 to 30%, while at 55 mM no inhibition pertained. Potassium and sodium ions at 55 mM had no effect on the calcium-independent phosphodiesterase from rat cerebrum. The results indicate that at normal intracellular concentrations of potassium ions the activity of the calcium-dependent phosphodiesterase is virtually completely dependent on the presence of calcium plus activator protein.
在没有激活蛋白的情况下，来自大鼠大脑的一种钙依赖性环核苷酸磷酸二酯酶受到各种单价阳离子的抑制。这种抑制作用迅速、易于逆转且呈浓度依赖性，100 mM的铯、铷或钾离子基本上能抑制所有基础酶活性，而100 mM的钠离子或锂离子仅产生适度抑制。阳离子抑制该酶的效力为Cs≥Rb＞K＞Na≥Li。钾离子使环鸟苷酸（cGMP）和环腺苷酸（cAMP）的表观Km分别增加3倍和5倍。在100 mM时，单价阳离子对由钙依赖性激活剂激活的酶的抑制作用仅为15%至30%，而在55 mM时则没有抑制作用。55 mM的钾离子和钠离子对大鼠大脑中不依赖钙的磷酸二酯酶没有影响。结果表明，在细胞内钾离子的正常浓度下，钙依赖性磷酸二酯酶的活性实际上完全依赖于钙和激活蛋白的存在。
