Palczewski K, Hargrave P A
R. S. Dow Neurological Sciences Institute of Good Samaritan Hospital and Medical Center, Portland, Oregon 97209.
J Biol Chem. 1991 Mar 5;266(7):4201-6.
A striking homology is observed between the regions 70-83 and 361-374 of the sequence of bovine arrestin and the calcium-binding loops of calmodulin and troponin C. However, the predicted alpha-helices flanking the calcium-binding site in calmodulin and troponin C are not present in arrestin. Direct measurements therefore were made in order to assess whether arrestin can bind calcium. We found that arrestin does not bind Ca2+ at physiological ionic strength, as determined by equilibrium dialysis, gel filtration, and fluorescence spectroscopy. Rapid and quantitative precipitation of arrestin occurs with Tb3+. The precipitation is reversed by EDTA and blocked by Mg2+ but not by Ca2+. Prompted by several reports, we also investigated whether nucleotides bind to arrestin. Neither ATP nor GTP binds under the conditions tested. Binding of arrestin to photolyzed, phosphorylated rhodopsin also does not influence the binding of calcium or nucleotides.
在牛抑制蛋白序列的70 - 83区域与361 - 374区域之间，观察到与钙调蛋白和肌钙蛋白C的钙结合环存在显著同源性。然而，钙调蛋白和肌钙蛋白C中钙结合位点两侧预测的α螺旋在抑制蛋白中并不存在。因此，进行了直接测量以评估抑制蛋白是否能结合钙。我们发现，通过平衡透析、凝胶过滤和荧光光谱测定，在生理离子强度下抑制蛋白不结合Ca2+。Tb3+能使抑制蛋白快速定量沉淀。这种沉淀可被EDTA逆转，并被Mg2+阻断，但不被Ca2+阻断。受几篇报道的启发，我们还研究了核苷酸是否与抑制蛋白结合。在所测试的条件下，ATP和GTP均不结合。抑制蛋白与光解的、磷酸化的视紫红质的结合也不影响钙或核苷酸的结合。
