Encyclopedia of Experiments: Biological Techniques
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Transcript
The mycobacterial cell wall contains different variants of mycolic acids - long-chain fatty acids with conserved alpha chains. Structural differences exist in their beta chains, resulting in the variations in the polarity of different mycolic acids.
To separate the variants using thin layer chromatography, or TLC - a liquid chromatography technique - take mycobacterial cell wall lipids in the desired organic solvent. Spot the lipids near the base of a TLC plate precoated with a thin layer of adsorbent material, which functions as the stationary phase.
Place the plate inside a jar containing an organic solvent - the mobile phase - ensuring the liquid level is below the sample spots to prevent premature diffusion of the mycolic acids.
During the run, the mobile phase rises through the tiny pores of the adsorbent layer on the plate via capillary action. Eventually, the mycolic acids dissolve in the solvent and travel upward.
More polar mycolic acid variants are transiently adsorbed by the polar stationary phase via intermolecular forces, hindering their upward movement. Less polar mycolic acids remain in the non-polar mobile phase and migrate further.
The differences in migration result in the variants of mycolic acid separating into discrete bands.
Upon completion, spray the dried plate with a phosphomolybdic acid stain. Heat the plate to reduce the stain in the presence of the lipids, imparting a dark green color to the bands.
