Cell-free synthesis of mycolic acids in Mycobacterium aurum: radioactivity distribution in newly synthesized acids and presence of cell wall in the system.
Distribution of radiolabelling in different parts of the newly synthesized mycolic acids, by a cell-free system from Mycobacterium aurum previously described, is examined, [1-14C]acetate being the precursor. By oxidation cleavage of mycolic acids and examination of the fragments, it was shown that acetate was not uniformly incorporated into the molecule: the methyl terminal part was not labelled, while the central fragments--between unsaturations or between oxygenated functions (oxo or ester) and unsaturations--presented the major part of radioactivity, suggesting the elongation of a preformed compound that the cell-free extract was unable to synthesize. Moreover, the side-chain R2-CH2-COOH was only weakly labelled compared to the central fragments. Since non-hydroxylated fatty acids were not synthesized by the system, it is suggested that de novo C18 fatty acids may be elongated with C2 units by the cell-free extract into C22 fatty derivative, only a low level of labelling being recorded (two C2 units for all the molecule). A scheme is proposed to summarize the main results. Identification of meso-DAP which is a characteristic amino-acid of the peptidoglycan in Actinomycetes and analysis of the profiles of total fatty esters, demonstrated that the cell-free extract is partly constituted by fragments of the cell wall as has already been noticed by examination of micrographs of the extract.
Lacave
C
C
Centre de Recherche de Biochimie et de Génétique Cellulaires, C.N.R.S., Université Paul Sabatier, Toulouse, France.
Quémard
A
A
Lanéelle
G
G
D000085:Acetates / Q000378:metabolism; D002250:Carbon Radioisotopes; D002473:Cell Wall / Q000378:metabolism; D002474:Cell-Free System; D002849:Chromatography, Gas; D006868:Hydrolysis; D009161:Mycobacterium / Q000378:metabolism*; D009171:Mycolic Acids / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D011865:Radioisotope Dilution Technique
D000085:Acetates; D002250:Carbon Radioisotopes; D009171:Mycolic Acids