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.