Molecular mechanisms underlying the high temporal resolution of photoreceptors.

高等动物感光细胞中的光电转导系统具有复杂的特性。首先是适应非常宽的背景照明的能力，其次是高时间分辨率，允许系统接收作为脉冲的光脉冲。PI研究了cGMP-磷酸二酯酶抑制亚基(PDE的g亚基；PG)的功能及其调节机制，以阐明导致光感受器高时间分辨率的分子机制。此外，在肌醇磷脂影响光感受器内源性蛋白激酶PG磷酸化的基础上，PI研究了光依赖性cGMP磷酸二酯酶的调节机制与杆状光感受器中肌醇磷脂代谢系统的关系。对于杆状光感受器中的内源性蛋白激酶，其分子量约为42-45 kDa，等电点为5.2。虽然PI在上述检查中对PG的功能有了新的认识，但由于其在来源器官中的含量较低，未能成功获得其特异性抗体和其基因克隆。此时，抑制磷酸二酯酶的脱辅酶是PG唯一的功能。然而，结果表明，通过与转导蛋白结合从PAb中释放PG会导致cGMP从PAb上的非催化结合部位释放。这一事实表明，光刺激PDE后cGMP的快速恢复至少部分归因于从Pab释放cGMP。此外，PI发现，肌醇磷脂代谢的抑制剂(U73122和新霉素)显著抑制杆状感光细胞外段光介导的cGMP水解。

Photo-electric transduction system in photoreceptor cells of higher animals possesses sophisticated characteristics. First is the ability for adaptation against an extraordinarily wide back-ground illumination, and second is a high temporal resolution that allows the system to receipt a photic pulse as a pulse. PI examined the function of an inhibitory subunit of cGMP-phosphodiesterase (g subunit of PDE ; Pg) and its regulatory mechanism to elucidate the molecular mechanism that attributes to the high temporal resolution of photoreceptors. In addition, on the basis of the finding that inositol phospholipids affect the phosphorylation of Pg by an endogenous protein kinase in photoreceptors, PI examined the relationship between the regulatory mechanism of light-dependent cGMP phosphodiesterase and inositol phospholipids metabolizing system in rod photoreceptors.As for the endogenous protein kinase of Pg in rod photoreceptors, its molecular weight was found to be approximately 42-45 kDa and pI value was 5.2. PI could not succeed to obtain its specific antibody nor a clone of its gene for its low content in source organ, though PI obtained new insight in the function of Pg during the examination described above. By this time, the inhibition of the apo-enzyme of phosphodiesterase is the only one function of Pg. However, it was shown that the release of Pg from Pab by binding with transducin results in the release of cGMP from the non catalytic binding site on Pab. This fact suggests that the quick recovery of cGMP after light stimulation of PDE is at least partly attributable to the release of cGMP from Pab. Furthermore, PI found that the inhibitors of inositol phospholipid metabolism (U73122 and neomycin) significantly inhibit light-mediated cGMP hydrolysis in rod photoreceptor outer segments.