Marcus R
Endocrinology. 1975 Feb;96(2):400-8. doi: 10.1210/endo-96-2-400.
Studies were carried out to characterize the cyclic nucleotide phosphodiesterase from rat calvaria. 25-40% of the total enzyme activity was membrane-bound. pH, magnesium, and temperature requirements conformed closely to those established for phosphodiesterase from other tissues. Kinetic evidence was found for dual enzyme activities with different substrate affinities for both the particulate and soluble enzyme. Apparent Kms for the soluble enzyme (3.5 times 10-6 and 2.5 times 10-5M) approximated those for the particulate enzyme (5.7 times 10-6 and 2.5 times 10-5M). L-Thyroxine, 10-5M, inhibited competitively the low- and high-Km enzymes from both the particulate and soluble fractions (Ki equals 1.7 times 10-5M). T4 was more potent an inhibitor than T3 with all enzyme fractions, but this relationship could be altered by adding protein to the incubation mixtures. Tests of diverse thyroid hormone analogues showed that 1) T4 and its derivatives were more potent than T3 and its analogues; 2) acetic and propionic acid derivatives were more potent than the thyronines; 3) "reverse T3," an antagonist of some T3 actions, also inhibited phosphodiesterase. These effects were not attributable to chelation, and were not duplicated by iodide or by other physiologically inactive thyroid hormone analogues.
开展了多项研究以表征来自大鼠颅骨的环核苷酸磷酸二酯酶。总酶活性的25 - 40%与膜结合。pH值、镁离子和温度要求与其他组织中磷酸二酯酶的相关要求密切相符。动力学证据表明，颗粒状酶和可溶性酶均具有对不同底物亲和力的双重酶活性。可溶性酶的表观Km值（3.5×10⁻⁶和2.5×10⁻⁵M）与颗粒状酶的表观Km值（5.7×10⁻⁶和2.5×10⁻⁵M）相近。10⁻⁵M的L - 甲状腺素竞争性抑制颗粒状和可溶性部分中的低Km和高Km酶（Ki等于1.7×10⁻⁵M）。在所有酶部分中，T4作为抑制剂比T3更有效，但通过在孵育混合物中添加蛋白质可改变这种关系。对多种甲状腺激素类似物的测试表明：1）T4及其衍生物比T3及其类似物更有效；2）乙酸和丙酸衍生物比甲状腺原氨酸更有效；3）“反式T3”（某些T3作用的拮抗剂）也抑制磷酸二酯酶。这些作用并非归因于螯合作用，并且碘化物或其他生理上无活性的甲状腺激素类似物无法复制这些作用。
