Molecular mechanism of light reception and regulation by visual pigments.

视色素在视细胞光转导过程中的作用是接收来自外界环境的光子并将信号传递给视网膜G蛋白转导素。本论文采用多种技术研究了视色素高光敏性的分子机制及其激活转导蛋白的有效能力，获得了以下结果：1.利用飞秒上转换光谱检测到视紫红质的荧光态，发现其衰减时间常数为60 fs。结合光学吸收光谱的傅里叶变换分析，从发色团异构化与发色团振动速度一样快的角度解释了这一超快过程。2.视紫红质的Glu-122被含有视锥色素的残基取代，使视紫红质的再电离和Meta Ⅱ的衰变速度转变为视锥色素的衰变速度。将Glu-122引入到视锥色素中，使视锥色素的性质变为视紫红质的性质。因此，122位的氨基酸残基是视杆细胞和视锥细胞色素的功能决定因子。3.利用时间分辨低温光谱技术，我们发现视紫红质的两个中间体Meta Ib和Meta II与transducin相互作用，但相互作用的方式不同：Meta Ib仅与转导蛋白结合，而meta II催化转导蛋白中的GDP-GTP交换。4.从cDNA测序、原位杂交和免疫组织化学实验来看，我们发现扇贝睫状光感受器细胞表达一种新的与Go型G蛋白偶联的视色素亚型。因此，一个新的，去介导的，光转导级联存在于扇贝睫状细胞。

The role of visual pigments in the phototransduction process of visual cells is to receive a photon from the outer environment and transfer the signal to a retinal G protein transducin. We have investigated the molecular mechanism of high photosensitivity of visual pigment and its efficient ability in activating transducin by various techniques, and following results were obtained :1.A fluorescent state of rhodopsin was detected by frmtosecond up-conversion spectroscopy and found that it decayd with a time constant of 60 fs. Combined with the analysis of the excited state of rhodopsin from a Fourier transform of optical absorption spectra, the ultrafast process was interpreted in terms of chromophore isomerization occuring as fast as vibrational motions of the chromophore.2.The replacement of Glu-122 of rhodopsin by the residue containing cone pigment converted rhodopsin's rates of reguneration and meta II decay into those of the cone pigment. The characteristics of cone pigment changed to those of rhodopsin by introduction of Glu-122 into cone pigment. Thus the amino acid residue at position 122 is a functional determinant of rod and cone visual pigments.3.Using time-resolved low temperature spectroscopy, we have found that two rhodopsin intermediates, meta Ib and meta II,interacted with transducin, but the manner of interaction with transducin is different : Meta Ib only binds to transducin, while meta II catalyzes a GDP-GTP exchange in transducin.4.From the sequencing of cDNAs, in situ hybridization, and immunohistochemical experiments, we have found that scallop ciliary photoreceptor cells express a novel subtype of visual pigment which coupled with Go type of G protein. Thus a novel, Go-mediated, phototransduction cascade is present in the scallop ciliary cells.