Spin-label studies of the sulfhydryl environment in bovine plasma albumin. 1. The N--F transition and acid expansion.
The environment of the sulfhydryl group in plasma albumin was previously characterized by employing spin-labels of varying chain lengths (Hull, H. H., Chang, R., & Kaplan, L. J. (1975) Biochim. Biophys. Acta 400, 132). It was established that the sulfhydryl is in a crevice approximately 10 A deep but this crevice was not identified further. We now report the results of titrating albumin through the acidic conformational transitions while monitoring the electron-spin resonance of the bound nitroxide. With short spin-labels a general change is observed as the pH is lowered but the N--F transition is not discernible. However, with a spin label previously shown to project to the lip on the crevice a clear N--F transition as well as the subsequent acid expansion are observed. These results indicate that the sulfhydryl is in the crevice, formed by the domains of albumin, which opens during the N--F transition. Further results indicate that bound fatty acids do not influence the integrity of the sulfhydryl environment at neutral pH.
D055598:Chemical Phenomena; D002621:Chemistry; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D008301:Maleimides; D011487:Protein Conformation; D012710:Serum Albumin, Bovine; D013113:Spin Labels; D013438:Sulfhydryl Compounds
D003497:Cyclic N-Oxides; D008301:Maleimides; D013113:Spin Labels; D013438:Sulfhydryl Compounds; D012710:Serum Albumin, Bovine