Being impermeable to folic acid, many bacteria must rely on their ability to synthesise folate from PABA, Pteridine, and glutamate in contrast the mammalian in cells cannot synthesise folic acid and must obtain preformed folate as a vitamin in their diet. The sulphonamides are structurally similar to PABA, the sulphonamides competitively inhibit dihydropteroate synthetase, the enzyme that catal...

There is little information on the origin of the pteridine ring of folic acid (1). The possibility that purines contribute to the biosynthesis of this part of the vitamin has been investigated earlier but could not be demonstrated in a number of microorganisms (2). In fact, attempts to demonstrate the conversion of purines to other naturally occurring pteridines have resulted in an impressive n...