Abstract: The focus of this project was to determine the method of catabolizing pyrimidines in cells of Pseudomonas syringae ATCC 12771. Enzyme assays of dihydropyrimidine dehydrogenase, dihydropyrimidinase and N-carbamoyl β-alanine amidohydrolase were performed under standard cell conditions and specific activities were determined for each enzyme with each auxotroph. Enzyme activities were determined for different nitrogen and carbon sources to observe the effects on their activity. It was demonstrated that glucose-ammonium sulfate and glucose-thymine grown cells showed repression of dihydropyrimidine dehydrogenase activity. It was observed that cells grown in both thymine and nitrogen-free medium showed repression of dihydropyrimidinase activity. It was also shown that succinate-uracil grown cells showed repression of the activity of the enzyme N-carbamoyl-β-alanine amidohydrolase. The primary reducing cofactor of dihydropyrimidine dehydrogenase was determined by comparative enzyme assays of varying substrates and cofactors. It was shown that the enzyme substrate uracil yielded the highest specific activity with each cofactor and the cofactor NADPH yielded the highest specific activity with each substrate. To verify the existence of NADPH in the cell, a pyridine nucleotide transhydrogenase enzyme assay was performed. The enzyme utilized NADPH in the cell extract to produce its product and it was then determined that the organism has NADPH available for use in its cell.