Biosynthetic pathways in Mycobacterium leprae.

: The scope of this paper is biosynthetic pathways which are found generally in living organisms. Many are present in M. leprae but some are lacking, perhaps reflecting the parasitic mode of existence of this microbe. The biosynthesis of nucleotides (the immediate precursors of nucleic acids) and fatty acids (intermediates in the biosynthesis of most if not all mycobacterial lipids) has been studied in detail in M. leprae. For the former, M. leprae appears incapable of synthesising its own purines de novo and thus depends upon the host for a source of the purine ring. It can synthesise pyrimidines, though enzymes for this activity are inhibited in the M. leprae organisms obtained from host tissue. For the latter, M. leprae is capable of fatty acid biosynthesis de novo, probably at a repressed level. However, a key enzyme, phosphotransacetylase, appears to be deficient.