Semi-micro methods for analysis of labile sulfide and of labile sulfide plus sulfane sulfur in unusually stable iron-sulfur proteins

Details are provided for a reproducible procedure for determination of labile sulfide in ironsulfur (FeS) proteins in the range of 1 to 3 nmol. Analyses are also presented on the most stable FeS protein so far reported. In this case denaturation with guanidine · HCl was used in the presence of dithiothreitol. The values obtained then also include any sulfane sulfur (S0) present.