title: Site of inhibitory action of isoniazid in the synthesis of mycolic acids in Mycobacterium tuberculosis.
abstract: The cellular mycolate synthetase activity of Mycobacterium tuberculosis H37Ra was previously shown to be very sensitive to isoniazid (Wang, L., and K. Takayama. 1972. Antimicrob. Agents Chemother. 2: 438-441). We have now examined the question of how isoniazid inhibits the synthesis of mycolic acids. The saponifiable 14-C-labeled lipids of control and isoniazid-treated cells (1.0 mug/ml, 60 min) were compared on a Sephadex LH-20 column, and it appeared that the synthesis of the intermediate-sized fatty acids was partially inhibited. These fatty acids were fractionated as their methyl esters by Sephadex LH-20 column chromatograp-y and gas-liquid (6% Dexsil) chromatography. Mass sectral analysis of the fractionated lipids revealed several series of fatty acids: fraction II, C39-C56; fraction III, C27-C40. The long-chain fatty acids in three kinds of isoniazid-treated cells were examined: (a) long-term exposure (48 hr, 0.5 mug/ml), (b) short-term exposure (60 min, 1.0 mug/ml), and (c) variable exposure at low concentration (0-90 min, 0.2 mug/ml). Both long- and short-term exposure experiments showed that isoniazid inhibited the synthesis of saturated fatty acids greater than C26 and of unsaturated fatty acids greater than C24. The variable-exposure experiment at low isoniazid concentration showed that the syntheses of mycolic acids and long-chain fatty acid fractions II and III were inhibited to the same extent. These fatty acids may thus be precursors of mycolic acids.
mesh_terms: D000085:Acetates / Q000378:metabolism; D002849:Chromatography, Gas; D002850:Chromatography, Gel; D005227:Fatty Acids / Q000096:biosynthesis; D007538:Isoniazid / Q000494:pharmacology*; D008970:Molecular Weight; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000378:metabolism*; D009171:Mycolic Acids / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013696:Temperature; D013997:Time Factors
chemical_list: D000085:Acetates; D005227:Fatty Acids; D009171:Mycolic Acids; D007538:Isoniazid