A miniaturized microtiter plate protocol for the determination of selenomethionine in selenized yeast via enzymatic hydrolysis of protein-bound selenium

This paper describes a simple/low volume enzymatic extraction method for selenomethionine (SeMet) determination in selenized yeast samples. In contrast to traditional methods which generally utilize large sample volumes consuming significant amounts of costly enzymes, the modified protocol employs a microtiter plate format allowing a reduction of the required sample volumes to 1 mL per extract. The extraction is performed in a parallel (5 x 4 = 20 position microtiter plate) reaction platform made out of sintered silicon carbide, fitted with standard disposable glass HPLC/GC vials. Due to the high thermal conductivity of silicon carbide, this set-up can be placed on a standard hotplate to accurately maintain the desired extraction conditions (37 degrees C, 20 h) for all positions of the microtiter plate. Hydrolysis of selenium-enriched yeast with a combination of protease XIV and lipase VII (ratio 2 : 1, w/w) using these low-volume conditions provided identical results to the more traditional high-volume method. The amount of SeMet was determined by HPLC/ICPMS and confirmed a high recovery rate for SeMet (93 +/- 2%, n = 3) for the certified reference material SELM-1.