A History of Iron Metabolism in the Mycobacteria - Iron Acquisition by the Genus Mycobacterium - page 13

Fig. 2.3 G Alan Snow (with
kind permission of The
Biochemical Society, UK)
The work, though, was extremely difficult. It was hindered by there being no
adequate assay for the growth factor as its structure was unknown and, although
it could bind to metal ions, this was not regarded of any particular significance.
Indeed, in the first full-length paper describing the isolation of mycobactin by
Francis et al. [ 28 ], more attention was given to the copper complex of mycobac-
tin and this was, in fact, the complex of mycobactin that was studied in detail.
Iron binding received only one mention in this seminal paper: “Ferric salts react
with mycobactin to give an intense reddish purple colour”. How these workers
missed the significance of iron binding to mycobactin, or failed to appreciate that
this would provide a simple assay for quantifying mycobactin, now seems strange
because the preparations of unchelated mycobactin readily form the red ferric
mycobactin complex, having a tenacity for iron binding is so strong that the myco-
bactin readily stripped iron from water, glassware and any materials containing
trace amounts of iron. However, as Snow was using such large quantities of cells
and extracting considerable amounts of mycobactin, the material was only turning
a light brown in color as clearly the amount of available iron was relatively small.
The early work on mycobactin was helped considerably by mycobactin adven-
titiously forming a crystalline aluminium complex [ 27 ] during its purification