AbstractBenzyl‐ITC (benzyl isothiocyanate) reacts preferentially with amino groups and sulfhydryl side chains of bovine sarcoplasmic proteins to form thiourea and dithiocarbamate derivatives, generally resulting in a decrease in solubility of the derivatives along a wide pH range. Under these conditions, it was also possible to show that secondary amine side chains, as found in tryptophan. also react with benzyl‐ITC. A quenching of tryptophan fluorescence intensity after interaction with benzyl‐ITC was also observed. Polyacrylamide gel electrophoresis (PAGE) experiments in the presence of urea indicated changes in electrophoretical mobility and in composition of subfractions. Changes in surface hydrophobicity and composition as determined by the ANS (8‐anilinonaphthalene‐1‐sulfonate) methode and RP‐HPLC were also observed. Polymerisation of protein molecules after reaction with benzyl‐ITC was documented using the SDS‐PAGE technique. These investigations showed that a group of subfractions belonging mainly to glycolytic enzymes and associated proteins with molecular weight between 38 – 70 kDa