Caretta A, Cavaggioni A, Sorbi R T
Biochim Biophys Acta. 1979 Feb 19;583(1):1-13. doi: 10.1016/0304-4165(79)90303-9.
The hydrolysis of cyclic guanosine monophosphate (cyclic GMP) and of guanosine triphosphate (GTP) by the broken rods of the frog retina after a flash of light have been studied in vitro with a constant perfusion method. The activation has an onset apparently instantaneous as observed with the existing possible time resolution of 3 s. The activation is followed by a partial inactivation that does not bring the activity back to the pre-flash level. GTP or the non-hydrolysable guanyl-5'-ylimidodiphosphate (GMP-PNP) is required for the normal light-activation of the phosphodiesterase and in its absence both the speed of activation and the sensitivity are greatly reduced. The activation speed, the sensitivity (threshold at approx. 0.00004% bleaching), and the kinetic constants do not exclude a direct role in the process of excitation for the phosphodiesterase and suggest a subsidiary but as yet undefined role for the GTPase.
利用连续灌注法在体外研究了蛙视网膜破碎杆状体在闪光后对环磷酸鸟苷（cGMP）和三磷酸鸟苷（GTP）的水解作用。在所观察到的3秒现有可能时间分辨率下，激活显然是瞬间开始的。激活之后是部分失活，失活不会使活性恢复到闪光前的水平。磷酸二酯酶的正常光激活需要GTP或不可水解的鸟苷-5'-亚氨二磷酸（GMP-PNP），在没有它们的情况下，激活速度和敏感性都会大大降低。激活速度、敏感性（约0.00004%漂白阈值）和动力学常数并不排除磷酸二酯酶在兴奋过程中起直接作用，并且表明GTP酶起辅助但尚未明确的作用。
