期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1980
卷号：77
期号：3
页码：1408-1411
DOI：10.1073/pnas.77.3.1408
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A light-activated GTPase that functions as a component of the rhodopsin-linked, light-activated phosphodiesterase (PDEase) system in vertebrate photoreceptors has been reported. In our efforts to purify photoreceptor GTPase we encountered another component (which we call "helper" or "H" component) whose presence is required for expression of light-activated GTPase activity. We report here the characterization of this heat-labile, macromolecular factor and that the presence of helper is absolutely required for light- and rhodopsin-dependent activation of photoreceptor GTPase. Of equal importance, we find that the "G" component (which requires the presence of H for expression of GTPase activity) can bind GTP and can support light- and GTP-dependent PDEase activation in the absence of H component. These data support a model in which GTP binding to G component is a necessary condition for PDEase activation. Hydrolysis of GTP at the G activator locus (an H-dependent activity) is a regulatory event which reverses PDEase activation. The complexity of this regulatory mechanism provides opportunities for signal modulation and amplification.
