Isabel M. Mountain

Determination of acid-soluble thiols and disulfides in transplanted animal tumors

Abstract The concentration of acid-soluble thiols and disulfides was measured in the deproteinized supernatant fractions of homogenates of seven transplanted mouse tumors and two rat tumors. Disulfides were determined after reduction to thiols with sodium borohydride in alkaline medium. Levels of both the reduced and oxidized forms of acid-soluble sulfur-containing peptides were of a similar magnitude. Certain details of the preparation of tissue samples were examined. Homogenization in an acid medium in the presence of high concentrations of sodium ethylenediaminetetraacetate is required to preserve the endogenous thiols from auto-oxidation. Reduction of disulfides with sodium borohydride must precede deproteinization to obtain high degrees of recovery of added oxidized glutathione standards. Reduction with zinc in an acid medium resulted in much lower and irregular recovery. Saturation with ammonium sulfate of tissue samples to be deproteinized did not improve the recovery of added internal standards of glutathione. Deproteinization of tissue samples with perchloric or sulfosalicylic acids produced superior results compared with samples deproteinized with metaphosphoric or trichloroacetic acids.