Abstract: A method of stabilising a biological sample including glutathione (GSH) and glutathione disulfide (GSSG), including a) providing the biological sample having GSH and GSSG; b) contacting GSH and GSSG of the sample with a maleimide to obtain maleimide-alkylated GSH; c) separating excess maleimide from maleimide-alkylated GSH and GSSG; d) contacting maleimide-alkylated GSH and GSSG with a reducing agent such as TCEP under conditions which allow reduction of GSSG by the reducing agent such as TCEP to obtain further GSH; and e) contacting maleimide-alkylated GSH and GSH with a heavy isotopologue of the maleimide to obtain a heavy isotopologue of the maleimide-alkylated GSH. A stabilised biological sample is provide containing maleimide-alkylated GSH and a heavy isotopologue thereof, as well as a mass-spectrometric method for quantifying maleimide-alkylated GSH and a heavy isotopologue thereof in a sample and a kit for stabilising a biological sample including GSH and GSSG for mass spectrometric analysis.

Abstract: A method of selective biooxidation to non activated carbon-hydrogen bonds of substances using a Geobacillus kaustophilus ‘Old Yellow Enzyme’ is provided”. It is shown that OYEs can be used to facilitate the biooxydation of substances, such as testosterone. It is also shown that OYE can introduce double bonds to form alpha, betaalpha, beta desaturated ketones. Furthermore, it is also shown that the use of OYEs allows for the production of oxidized substances in one step reactions, which are otherwise not accessible or only accessible after complex and inefficient multi-step reactions. In addition, the OYE used shows high stability (e.g. at high temperature, or in long lasting bioconversions). An exemplary embodiment is provided showing the use of an OYE to convert testosterone to 6?-hydroxytestosterone.