The Sulfhydryl Content of Normal and Abnormal Human Sera.∗

The sulfhydryl content of serum proteins has been quantitatively determined through an adaptation of an amperometric titration. Among normal adults, the values noted, expressed as milligrams of cysteine, were uniform, reproducible and averaged 6.5±0.2 mg per 100 ml serum or 5.5±0.3 mg per gram serum nitrogen. The albumin component of serum contained 80% of the total sulfhydryl. The addition of desoxyribonucleic acid, creatine or formaldehyde did not change the sulfhydryl content of the serum. The addition of an SH reagent such as para-chloro-mercuri-benzoate abolished all reactant groups measured with this method.Sera obtained from patients with various diseases showed a significant reduction in the sulfhydryl available for this titration. This quantitative reduction in sulfhydryl was still evident when corrected for differences in the albumin and globulin components and thus represented a qualitative change in the serum proteins. At the present time, the alteration in the sulfhydryl content of serum or its components is not characteristic enough to permit specific differentiation among the neoplastic, metabolic, or infectious diseases. The possible application of serial serum sulfhydryl determinations in animals and patients may be of value as an objective indicator of response and for study of the mechanism of action of chemotherapeutic and other agents.