Enzymatic probe sonication:: Enhancement of protease-catalyzed hydrolysis of selenium bound to proteins in yeast

This paper describes the dramatic activity enhancement of two proteolytic enzymes (protease XIV and subtilisin) when treated with an ultrasonic probe and their application to total Se determination and Se speciation in biological samples. Total Se extraction from enriched yeast is performed with 10 mg of yeast plus 1 mg of protease with a sonication time of 5 s, whereas 30 s is needed for extracting selenomethionine. In both cases, aqueous media was used. This spectacular finding is important because the enzymatic procedure usually requires a long treatment period at 37 degreesC. In addition to this major advantage, no control temperature is needed and the risk of species interconversion is drastically reduced or inhibited (the same Se species were detected after different sonication times). Moreover, the extraction is performed in water, minimizing contamination risk and without further pH adjustment. The new sample treatment proposed has been successfully applied to selenium speciation in yeast using chromatographic separation (HPLC) coupled to inductively coupled plasma-mass spectrometry.