Metabolism of pyrithiamine by the pyrithiamine-requiring mutant of Staphylococcus aureus.

1. A mutant strain of Staphylococcus aureus that requires pyrithiamine for its optimum growth was found to utilize pyrithiamine during the exponential phase of growth. 2. Pyrithiamine was deaminated by the organism to form oxypyrithiamine, the reaction being enzymic with no cofactor requirement. 3. On prolonged incubation of S. aureus A cultures, the concentration of deaminating enzyme increased in the culture broth, from which pyrithiamine-deaminating enzyme could be isolated by solvent fractionation. 4. Oxypyrithiamine is not a competitive analogue of thiamine although it inhibited the growth of the parent strain of S. aureus; the inhibition index of this compound, however, was lower than that of pyrithiamine.