Comparison between thymidylate synthase B of Bacillus subtilis ATCC6633 and 168

Bacillus subtilis 168 possesses two thymidylate synthase genes: thyA and thyB, encoding for a thermolabile and a thermostable enzyme respectively. B. subtilis ATCC6633 also possesses two thy genes, both producing thermostable enzymes. A comparison of the thymidylate synthase B amino acid sequences from the two strains shows, among others, a Pro to Ala mutation which may affect the dUMP binding site. The apparent Km and Vmax values for dUMP and tetrahydrofolate were determined at a permissive temperature for both enzymes. The kinetic data showed a significant difference in the Km, but not in the Vmax, for dUMP between the two enzymes. The Km and Vmax for tetrahydrofolate were very similar.