Question

1.Prontosil showed anti-bacterial activity in patients in vivo but not in vitro. What is the reason for this?

2.List two possible ways by which prontosil/sulfanilamide acts as a reversible competitive inhibitor of folic acid biosynthesis. Draw chemical structures as may be necessary to illustrate your point.

3.Why are sulphonamide selective to bacteria?

Answer 1

1)

•Pentosil is a drug belongs to sulphonamide group and has antibacterial properties. It has been observed that it do not show antimicrobial activity in the test tube (in-vitro). The reason behind this given by the Bovet is that when it go into body, it get converted into an antimicrobially active form like sulfanilamide. This act as the active factor for the drug.

2)

•For bacterial enzyme dihydropteroate synthetase, sulfonamide act as a competitive inhibitor. It use PABA for the folic acid synthesis. The inhibited reaction is necessary for the synthesis of the folic acid in the organism. Without this there will be no replication in the bacteria.

3)

•It is very clear that there is the interfere done by the sulfonamides in the formation of folic acid in bacteria. There is no sequence of any enzyme reaction that lead to folic acid in mammalian cells. They are dependent on external source. This is the basis for the selective action of sulfonamides on bacteria. This is also the reason that they are selective to bacteria.