Determination of rhodanese activity by tetrazolium reduction

A colorimetric method for the assay of rhodanese activity based on the continuous determination of the sulfite product is described. 5-Ethylphenazinium ethyl sulfate is used as the intermediate electron carrier between sulfite and nitroblue tetrazolium to produce the colored reduced species. The present method is more sensitive than the usual procedure based on the colorimetric determination of thiocyanate. Furthermore, the color developed by nitroblue tetrazolium reduction affords a straightforward means to locate rhodanese activity in polyacrylamide gels.