A NEW STRUCTURAL TRANSITION OF SERUM-ALBUMIN DEPENDENT ON THE STATE OF CYS34 - DETECTION BY H-1-NMR SPECTROSCOPY

1. Reactions of fatty-acid-free bovine serum albumin and recombinant h uman albumin with a range of antiarthritic gold(I) complexes [auranofi n, deacetylated auranofin, triethylphosphinegold(I) chloride] and rela ted thiols (thioglucose, tetraacetylthioglucose, glutathione, dithioth reitol) have been investigated using H-1-NMR spectroscopy. 2. In react ions of albumin with auranofin, tetraacetylthioglucose and dithiothrei tol, release of cystine was detected, whereas for deacetylated auranof in, thioglucose and glutathione, mixed disulphides with cysteine were produced. It has been previously proposed that Cys34 of human and bovi ne serum albumins is partly blocked by disulphide formation with cyste ine and glutathione. The above reactions lead to deblocking by thiol-d isulphide interchange reactions. No release of glutathione from albumi n was detected. 3. Changes in the His H epsilon 1 regions of the H-1-N MR spectra show that albumin exists in two structural forms dependent on whether the side-chain of Cys34 is a free thiolate, or blocked by g old(I)triethylphosphine, by disulphide formation with cysteine or by a nother form of oxidation. We propose that Cys34 is either in a buried or in an exposed environment; the possible molecular basis of the stru ctural change is discussed. 4. The relationship between reactions at C ys34, cysteine release, and the observed structural transition are dis cussed in terms of chrysotherapy, albumin metabolism and the use of go ld(I) as a heavy atom derivative in X-ray crystallographic studies of albumins.