Studies on serum albumin and hemoglobin: the two principal transport proteins in blood
Abstract (Summary)The structural changes in human serum albumin upon its binding of fatty acid anions were investigated. Red-shifts in HSA's UV spectrum following the addition of long chain fatty acid (LCFA) anions reflect a major change in its conformation. Similar but smaller changes after the addition of decanoate and other medium chain-length fatty acid (MCFA) anions reflect either a smaller or a less complete conformation change. Dansylsarcosine's fluorescence, is sharply reduced by low levels of MCFA anions known to bind to the same site. Similar levels of LCFA anions have only a small effect on its fluorescence but suppress it at higher levels. Prominent and characteristic spectral changes accompanying PLP's reaction with fatty acid-free HSA are only slightly affected by four equivalents of LCFA anion but almost completely eliminated by five equivalents. Similar levels of MCFA anions have little affect on PLP's reaction with HSA but gradually suppress it at higher levels. These results appear to reflect a concerted change in HSA's conformation upon the simultaneous binding of five LCFA anions. Isothermal titrations with LCFA and MCFA anions suggest the former bind cooperatively whereas the latter do not. The thiol content of fresh plasma HSA undergoes a biphasic decrease. The initial rapid phase was partially inhibited by superoxide dismutase, catalase, a mixture of both, to a lesser extent by allopurinol, and to a still lesser extent by EDTA, suggesting it is due mainly due to the reaction of Cys-34 of HSA in plasma with reactive oxygen species (especially hydrogen peroxide and superoxide) and free cysteine, cysteinylglycine and reduced glutathione in plasma. The S-nitroso derivatives of glutathione, N-acetyl-penicillamine, L-cysteine, 3-mercaptopropionic acid and 2-mercaptoethanol were shown to react with bovine oxyhemoglobin at different rates and with different kinetics. When RSNOs were in excess, they were shown to participate in both the transnitrosation reaction with the –SH groups of â Cys93 and the oxidation reaction with the hemes of oxyhemoglobin, which when combined with results from the Saville assay indicating the production of S-nitrosylated protein(s), suggested that excess RSNOs react with HbO2 â chains with two pathways and with á chains with only one pathway.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2004