Aspartate semialdehyde dehydrogenase (ASD) catalyses the reversible conversion of b-aspartyl phosphate to aspartate β-semialdehyde (ASA) and inorganic phosphate (P_i) using NADPH as the cofactor. ASA is subsequently utilised for the synthesis of several important bacterial metabolites, including DAP, DPA, Ile, Lys, Met and Thr. Interestingly, Bacillus anthracis encodes two asd gene, designated asd1 and asd2. Bioinformatics analysis suggests that the products of asd1 and asd2 share 65% sequence identity, but little is known about the expression, structure and function of ASD1 and ASD2.  The hypothesis of this project is that B. anthracis requires two asd genes in order to provide greater carbon fluxes of ASA for the synthesis of key metabolites during sporulation and vegetative growth. The aims of this project are to clone, express, purify and characterise the expression, function and structure of ASD1 and ASD2. We have successfully cloned and expressed milligram quantities of the recombinant enzymes and show that they possess ASD catalytic activity. We are now performing in-depth biochemical and biophysical analyses to compare the expression and structure-function relationship of ASD1 and ASD2.  This study will offer insight into the biological importance of asd gene duplication in a significant bioterrorism agent and agricultural pathogen..