30] Analysis of acid-labile sulfide and sulfhydryl groups

Abstract

Publisher Summary This chapter analyzes the acid-labile sulfide and sulfhydryl groups. The demonstration of the occurrence of “labile sulfide” or inorganic sulfide in plant and clostridial ferredoxins is an important factor in the ultimate recognition of the existence of a class of proteins now termed “iron–sulfur” proteins. The discovery of most of the individual proteins that have recognized as iron–sulfur proteins is based on their content of nonheme iron. Characterization of the labile sulfide of iron–sulfur proteins is now firmly established on the basis of reconstitution experiments, X-ray analysis of clostridial ferredoxin, and the synthesis of model compounds. Sulfur atoms of the cysteinyl residues of the protein also participate as ligands of the iron atoms of the [Fe–S] clusters. The quantitative determination of labile sulfide in proteins is carried out, for the most part, by the “methylene blue method,” with reagents originally described by Fischer, and more recently by Fogo and Popowsky for the determination of hydrogen sulfide, and the conditions described for the determination of sulfide in clostridial ferredoxin.