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.
Centre de Recherche de Biochimie et de Génétique Cellulaires, C.N.R.S., Université Paul Sabatier, Toulouse, France.
C
C
Lacave
A
A
Quémard
G
G
Lanéelle
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