Akhtar R A, Abdel-Latif A A
Biochim Biophys Acta. 1978 Nov 10;527(1):159-70. doi: 10.1016/0005-2744(78)90265-6.
The rabbit iris smooth muscle has been shown to contain triphosphoinositide phosphomonoesterase (phosphatidyl-myo-inositol-4,5-bisphosphate phosphohydrolase, EC 3.1.3.36) and phosphodiesterase (triphosphoinositide inositoltrisphosphohydrolase, EC 3.1.4.11) activities. Under our experimental conditions about 77% of the phosphomonoesterase and 61% of the phosphodiesterase activities were localized in the particulate fraction. The kinetic properties of the enzymes in the microsomal fraction were examined. The enzyme preparation was specific to polyphosphoinositides; it did not attack phosphatidylinositol under the present assay condition. The effects of Ca2+ and Mg2+ were also studied. Although the microsomal enzymes did not require added divalent cations for their activities, both the phosphomonoesterase and phosphodiesterase were appreciably inhibited by 1 mM EDTA. Phosphodiesterase and phosphomonoesterase were stimulated by Ca2+ and Mg2+, respectively. The demonstration of triphosphoinositide phosphodiesterase in the iris muscle, coupled with the findings that this enzyme is activated by Ca2+ and is not influenced by acetylcholine add further support to our previous conclusion (J. Pharmacol. Exp. Ther. (1978) 204, 655--668; J. Neurochem. (1978) 30, 517--525) that an increased Ca2+ influx, following the interaction between the neurotransmitter and its receptor, could act to stimulate the phosphodiesterase, thus leading to increased triphosphoinositide breakdown and increased phosphatidic acid via increased diacylglycerol.
已证明兔虹膜平滑肌含有三磷酸肌醇磷酸单酯酶（磷脂酰肌醇 - 4,5 - 二磷酸磷酸水解酶，EC 3.1.3.36）和磷酸二酯酶（三磷酸肌醇肌醇三磷酸水解酶，EC 3.1.4.11）活性。在我们的实验条件下，约77%的磷酸单酯酶活性和61%的磷酸二酯酶活性定位于微粒体部分。对微粒体部分中酶的动力学性质进行了研究。该酶制剂对多磷酸肌醇具有特异性；在目前的测定条件下它不作用于磷脂酰肌醇。还研究了Ca2+和Mg2+的影响。虽然微粒体酶的活性不需要添加二价阳离子，但1 mM EDTA可显著抑制磷酸单酯酶和磷酸二酯酶。磷酸二酯酶和磷酸单酯酶分别受到Ca2+和Mg2+的刺激。虹膜肌中三磷酸肌醇磷酸二酯酶的证明，再加上该酶被Ca2+激活且不受乙酰胆碱影响这一发现，进一步支持了我们先前的结论（《药理学与实验治疗学杂志》（1978年）204, 655 - 668；《神经化学杂志》（1978年）30, 517 - 525），即神经递质与其受体相互作用后Ca2+内流增加可刺激磷酸二酯酶，从而导致三磷酸肌醇分解增加，并通过二酰基甘油增加导致磷脂酸增加。
