Synthesis and properties of 5-membered heterocyclic disulfides: application for enzyme modification

Synthesis of the disulfides 2,2'-dithiodithiazole, 2,2'-dithiobis(4-methylthiazole), and 5,5'-dithiobis(3-methylisothiazole), which are thiol-specific reagents, is described and the uv-absorption spectra of the disulfides and corresponding thiols and/or thiones are presented. The utility of these and several other reagents for the modification of thiol groups in enzymes has been demonstrated with lactate dehydrogenase and malate dehydrogenase and compared with the frequently applied modification reagents 5,5'-dithiobis(2-nitrobenzoic acid) and 2,2'-dithiodipyridine. The 5-membered heterocyclic disulfides permit the spectrophotometric determination of all sulfhydryl groups of malate dehydrogenase and lactate dehydrogenase without requiring their prior denaturation. Application of these reagents makes possible the determination of SH groups in the pH range less than or equal to 7.