Kurtz M J, Edwards R B, Schmidt S Y
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, MA 02114.
Exp Eye Res. 1987 Jul;45(1):67-75. doi: 10.1016/s0014-4835(87)80079-9.
Kinetically distinct classes of cyclic AMP (cAMP) and cyclic GMP (cGMP) phosphodiesterase activities (PDEs) were detected in homogenates of cultured pigment epithelium (PE) from both normal and Royal College of Surgeons (RCS) rats. PDE activities with apparent low Michaelis constants (Low Km cAMP- and cGMP-PDEs) were associated with the supernatant, while PDE activities with apparent high Michaelis constants (high Km cAMP- and cGMP-PDEs) were slightly higher in the pellet than in the supernatant after ultracentrifugation (100,000 g). Activity of the low Km PDEs was significantly reduced while that of high Km PDEs was not affected by known inhibitors of PDE. In both normal and RCS rat PE low Km PDEs required calcium and magnesium ions for optimal activity while the high Km PDEs required neither. In homogenates of cultured RCS rat pigment epithelium (PE), the kinetic parameters for cAMP- and cGMP-PDEs were comparable to normal, with the exception of the Km value of the low Km cGMP-PDE. This Km value was two-fold higher in the RCS compared with the normal (indicative of a reduced affinity for cGMP). It remains to be determined if the reduced affinity for cGMP in the RCS PE is related to the genetic defect which is expressed as a deficiency in the phagocytosis of outer segments by these cells.
在正常大鼠和皇家外科学院（RCS）大鼠的培养色素上皮（PE）匀浆中检测到了动力学上不同类别的环磷酸腺苷（cAMP）和环磷酸鸟苷（cGMP）磷酸二酯酶活性（PDEs）。表观米氏常数较低的PDE活性（低Km cAMP - 和cGMP - PDEs）与上清液相关，而表观米氏常数较高的PDE活性（高Km cAMP - 和cGMP - PDEs）在超速离心（100,000 g）后沉淀中的活性略高于上清液。低Km PDEs的活性显著降低，而高Km PDEs的活性不受已知PDE抑制剂的影响。在正常和RCS大鼠PE中，低Km PDEs需要钙离子和镁离子以达到最佳活性，而高Km PDEs则不需要。在培养的RCS大鼠色素上皮（PE）匀浆中，cAMP - 和cGMP - PDEs的动力学参数与正常情况相当，但低Km cGMP - PDE的Km值除外。与正常情况相比，RCS中的该Km值高出两倍（表明对cGMP的亲和力降低）。RCS PE中对cGMP亲和力的降低是否与这些细胞中外段吞噬作用缺陷所表现出的遗传缺陷有关，仍有待确定。
