Quantitative determination of biological sulfhydryl groups by postcolumn derivatization and elucidation of microheterogeneity of serum albumins

A quantitative analytical system for biological sulfhydryl compounds has been developed using an ion-pair reagent with isocratic elution and an on-line postcolumn derivatization with Ellman-type reagents. As human or bovine serum albumin has 35 cysteinyl residues, one cysteinyl residue exists as a free sulfhydryl moiety, and this gives rise to the microheterogeneity in serum albumin. Here we report for the first time the quantitative characterization of the microheterogeneity of serum albumin. Cysteine was found to be the major molecule attached to the sulfydryl group of the serum albumins. Although glutathione could not be detected, the Cys-Gly element of glutathione was found. Freshly prepared human serum albumin from healthy volunteers contained 0.46 nmol of Cys/mL of serum, 0.24 nmol of Cys-Gly/mL of serum, and very small amounts of glutathione (0.02 nmol/ml).