Submicrodeterminations of thiols, disulphides and thiol esters in serum by using o-hydroxymercuribenzoic acid and dithiofluorescein.

1. Methods are described for selective estimation of thiols, disulphides and thiol esters in standard solutions and in serum. The methods are based on the reaction with the excess of o-hydroxymercuribenzoic acid (HMB) in alkaline solution with subsequent addition of dithiofluorescein in excess and determination of the extinction at 588mmu. The sensitivity of the methods amounts to 1.5x10(-9)g.equiv. in 5ml. of final solution. Of results obtained on standard solutions 80% have the errors within the range +/-4%. 2. It has been found that serum contains an unidentified substance (substance X) producing green complexes with dithiofluorescein which undergo decomposition on addition of formaldehyde. The correction for substance X must be estimated in a separate sample and taken into account. The concentration of substance X can be calculated from extinctions measured at 588mmu and 635mmu in the presence of dithiofluorescein in excess. 3. The selective determination of thiols and disulphides is based on different reaction rates with formaldehyde. The complexes between HMB and cysteine can be selectively decomposed by formaldehyde, and free glutathione can be selectively removed by formaldehyde in the presence of protein thiols. 4. Thiols are determined in the presence of triethylamine, thiols plus disulphides in the presence of triethylamine and sulphite, and thiols plus thiol esters in the presence of dimethylamine, with subsequent addition of ammonium sulphate.