11-cis-retinal and zinc-chloride

To explore peptide hormone-induced conformational changes, we attempted to engineer a metal-ion binding site between the cytoplasmic loops CD and EF in the angiotensin II type 1 (AT(1)) receptor. We constructed 12 double and six triple histidine mutant receptors, and tested the ability of each mutant and the wild-type to activate inositol phosphate (IP) production with and without ZnCl(2). Inhibition by ZnCl(2) in the double and triple His mutant receptors was not significant, but these mutations directly decreased the IP production. Systematic analysis of single His mutants demonstrated that the loop CD-mutants displayed 52-74% inhibition of IP production, whereas the loop EF-mutants did not affect IP production. These results indicate that the cytoplasmic loop CD-segment from Tyr(127) to Ile(130) is important for G(q/11) activation by the AT(1) receptor.

Topics: Amino Acid Sequence; Amino Acid Substitution; Angiotensin II; Angiotensin Receptor Antagonists; Animals; Binding Sites; Cattle; Chlorides; COS Cells; Heterotrimeric GTP-Binding Proteins; Histidine; Inositol Phosphates; Kinetics; Losartan; Models, Molecular; Molecular Sequence Data; Mutation; Protein Structure, Secondary; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin; Rhodopsin; Sequence Alignment; Signal Transduction; Thermodynamics; Zinc Compounds

There is a high concentration of zinc in ocular tissue, especially the retinachoroids, and the presence of physiological levels of zinc in these tissues seems essential for their normal function. The purpose of our study was to clarify this point using electroretinogram (ERG) recordings and spectrophotometer measurements before and after zinc treatment in a bullfrog's eye. The optimal zinc concentration used in this experiment was 1 microM ZnCl2, 100 microliters/6 ml ringer solution, with the result that the total zinc concentration in the ringer solution was 16.4 nM. To determine the effects of zinc on the retinal function, the changes of ERG parameters, such as threshold, a-, b- and c-waves and absorption spectra were observed before and after zinc treatment. It is noteworthy that high concentrations of zinc are present in the retina and the retinal pigment epithelium. Our results indicate that zinc treatment elevated the dark-adapted ERG threshold, all of the peak amplitudes of ERG were increased and rhodopsin regeneration was accelerated during visual adaptation. In spectral scans, absorbance increment due to zinc treatment was shown over the whole range of spectral scanning (300 nm-750 nm). We believe that zinc, which is abundant in the retina and the retinal pigment epithelium particularly, is an essential factor for the visual process and may be required to improve visual sensitivity during visual adaptation.

Topics: Animals; Chlorides; Dark Adaptation; Electroretinography; Rana catesbeiana; Retina; Rhodopsin; Sensory Thresholds; Visual Perception; Zinc Compounds