Gopal V K, Francis S H, Corbin J D
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-0615, USA.
Eur J Biochem. 2001 Jun;268(11):3304-12. doi: 10.1046/j.1432-1327.2001.02233.x.
To date, relative cellular levels of cGMP and cGMP-binding proteins have not been considered important in the regulation of smooth muscle or any other tissue. In rabbit penile corpus cavernosum, intracellular cGMP was determined to be 18 +/- 4 nM, whereas the cGMP-binding sites of types Ialpha and Ibeta cGMP-dependent protein kinase (PKG) and cGMP-binding cGMP-specific phosphodiesterase (PDE5) were 58 +/- 14 nM and 188 +/- 6 nM, respectively, as estimated by two different methods for each protein. Thus, total cGMP-binding sites (246 nM) greatly exceed total cGMP. Given this excess of cGMP-binding sites and the high affinities of PKG and PDE5 for cGMP, it is likely that a large portion of intracellular cGMP is associated with these proteins, which could provide a dynamic reservoir for cGMP. Phosphorylation of PDE5 by PKG is known to increase the affinity of PDE5 allosteric sites for cGMP, suggesting the potential for regulation of a reservoir of cGMP bound to this protein. Enhanced binding of cGMP by phosphorylated PDE5 could reduce the amount of cGMP available for activation of PKG, contributing to feedback inhibition of smooth muscle relaxation or other processes. This introduces a new concept for cyclic nucleotide signaling.
迄今为止，cGMP和cGMP结合蛋白的相对细胞水平在平滑肌或任何其他组织的调节中尚未被认为是重要的。在兔阴茎海绵体中，细胞内cGMP被测定为18±4 nM，而通过针对每种蛋白质的两种不同方法估计，Iα型和Iβ型cGMP依赖性蛋白激酶（PKG）以及cGMP结合的cGMP特异性磷酸二酯酶（PDE5）的cGMP结合位点分别为58±14 nM和188±6 nM。因此，总的cGMP结合位点（246 nM）大大超过总的cGMP。鉴于cGMP结合位点的这种过量以及PKG和PDE5对cGMP的高亲和力，很可能细胞内大部分cGMP与这些蛋白质相关联，这可能为cGMP提供一个动态储存库。已知PKG对PDE5的磷酸化会增加PDE5变构位点对cGMP的亲和力，这表明存在调节与该蛋白质结合的cGMP储存库的潜力。磷酸化的PDE5对cGMP的增强结合可能会减少可用于激活PKG的cGMP量，从而导致对平滑肌松弛或其他过程的反馈抑制。这引入了一种关于环核苷酸信号传导的新概念。
