Salmonella are a leading cause of food borne illnesses in humans. Even though symptoms are often mild, these enterobacteria are responsible for over 200,000 deaths worldwide every year. There is considerable concern over the emergence of drug-resistant strains of Salmonella. Lactate dehydrogenase (LDH) from Salmonella typhi is believed to be an essential enzyme for the bacteria and hence a potential drug target. This enzyme is a D-speCific LDH and hence belongs to a class of enzymes much less studied than the more common L-specific LDHs. In this study the expression, structural and functional characterisation of the Salmonella D-LDH enzyme is reported. Crystal structures of the enzyme indicate a number ' of unusual features within its active site that may facilitate specific targeting by novel inhibitors . . Preliminary enzymatic activity data confirm the expected Dspecificity of this enzyme, and that oxamic acid is a weak inhibitor with a Ki of 10.5 mM. The crystal 'structures and enzymatic analyses provide a basis for structure-based design of novel inhibitors. This thesis also describes preliminary studies aimed at determining the structure of a cytochrome P450 enzyme from Jeotga/icoccussp. (oleTJE). This enzyme, a member of the CYP152 family, has peroxygenase activity and can be used to produce alkenes (olefins). It is therefore of interest for the development novel biofuels. Its crystallization is reported, although initial attempts to determine its crystal structure have so far been unsuccessful.