[Quantitative cytospectrometrical determination of protein sulfhydryl groups and reactive disulfide groups by the...

Protein sulfhydryl groups are histochemically demonstrated by reacting with DDD followed by coupling with Fast blue B. The molar absorptivity of the formed azo dye is 19000 per mole SH reacted. DDD simultaneously reacts with protein-SH- and -SS-groups. However, the reaction with SH-groups is approximately 1000 times faster than that observed with SS-groups. With Ehrlich ascites tumour cells the reaction of DDD with SH-groups is completed within 7 h while the reaction of DDD with SS-groups needs 14 days for completion. Due to the extreme difference in the reaction rates protein bound SH-groups as well as reactive SS-groups can be estimated quantitatively by cytospectrophotometrical methods. The cells investigated showed an average SH-content of (1,30 +/- 0,03) X 10(-14) M SH/cell while the average content of reactive SS-groups was (1,59 +/- 0,28) X 10(-14) M SS/cell. In addition it was found that especially the amount of reactive SS-groups per cell is not constant but exhibits seasonal variations.