Characterization of carbon disulfide binding in blood and to other biological substances

Free and bound forms of CS2 are present in subjects exposed to CS2. In rats exposed to 2 mg/liter (approximately 640 ppm) of CS2 for 4 hr, concentrations of acid-labile CS2 (AL CS2, a form of bound CS2 that can be recovered from biological samples by acid treatment) in plasma and red blood cells (RBCs) increased linearly with exposure time. The majority (90%) of the blood AL CS2 was present in the RBCs. About 95% of the AL CS2 in plasma and in RBCs of exposed rats was found in the precipitates after treatment with ammonium sulfate. Incubation of fractionated human RBC lysates with CS2 showed that CS2 binding in these fractions was proportional to the hemoglobin concentration. These observations show that in blood, CS2 binds (in the form of AL CS2) mainly to hemoglobin and to a small extent to other blood proteins. Binding of CS2 to small molecules, including amino acids, accounted for only a small fraction of blood AL CS2. In in vitro studies, CS2 also bound to human albumin, gamma-globulin, and horse heart myoglobin. It was also found that CS2 binds to amino and sulfhydryl compounds at physiological pH. Plasma incubated with CS2 was found to chelate copper. Chelation of copper-containing enzyme by the reaction products of CS2 and biological amines has been observed and has been proposed as one of the mechanisms by which CS2 induces neurotoxicity (M.J. McKenna and V. DiStefano, 1977b, J. Pharmacol. Exp. Ther. 202, 253-266). Radioisotope studies showed that a substantial portion of the radioactivity could not be released from 14CS2-treated plasma and serum upon acid treatment at elevated temperature. These studies suggest the existence of non-acid-labile bound CS2, besides AL CS2, in plasma and serum treated with CS2.