A History of Iron Metabolism in the Mycobacteria - Iron Acquisition by the Genus Mycobacterium - page 14

and passage through a column of chromatographic alumina. This allowed the
team to carry out some X-ray crystallography giving a suggested molecular
weight of about 914. This was subsequently revised to 870 with the formula of
C 47 H 75 O 10 N 5 . To work out the structure of such a large molecule, however, was
then a considerable and daunting task. Also, as mentioned above, Snow and his
colleagues had found that it was extremely difficult to assay mycobactin during its
purification processes. Initially, assays for its presence had to rely on its growth-
stimulating properties for M. paratuberculosis which were slow and extremely
tedious even with improved techniques [ 29 ]. There were, however, suggestions by
Antoine et al. [ 30 ] and Reich and Hanks [ 31 ] that Arthrobacter terregens , which
also required a 'terregens factor' for growth, might be a more suitable organism
for the bioassay of mycobactin as it could be grown in about 3 days or so. This
bacterium was, though, much less sensitive to mycobactin than M. paratuberculo-
sis [ 26 ] and was also responsive to growth factors other than mycobactin. It there-
fore does not appear to have been used to any great extent by Snow himself.
The initial major effort that had been put into the pharmacological aspects of the
project appears to have dissipated somewhat by the very early 1950s and the origi-
nal authors of the 1953 paper [ 28 ] do not appear, even in the acknowledgements, of
the next papers that were published on the structure of mycobactin in 1954 [ 32 , 33 ].
Perhaps the discovery of streptomycin in 1943 as the first anti-tuberculosis antibiotic
followed by its general availability in the late 1940s, together with the arrival of PAS
( p -aminosalicyclic acid) as a second anti-TB agent in 1953, may have influenced the
senior managers of ICI that the future of anti-tuberculosis treatment would lie with
antibiotics and not with problematic, and still to be synthesized, possible antagonists
of a still largely uncharacterized mycobactin. But for whatever reason, Alan Snow
then was the person who almost single-handedly elucidated the structures not only
of the mycobactin from M. phlei but many other ones as well (Fig. 2.4 ).
The initial description of a possible structure for mycobactin form M. phlei was
given in the December 1954 issue of the Journal of the Chemical Society [ 33 ].
However, there was a problem with working out how one of the hydrolytic prod-
ucts of mycobactin, 2-amino-6-hydroxyaminohexanoic acid, was orientated in
the molecule. Two possible structures for it were offered. It was though another
11 years before this issue was resolved. No full-length papers were published by
Snow or any other person on the mycobactins from 1954 to 1965 though there was
a short preliminary communication made in 1961 to a meeting of the Biochemical
Society in the UK [ 34 ] concerning the isolation of the mycobactin from M. tuber-
culosis . But it seems likely that the mycobactin project was now de-prioritized
roundabout this time and, in a letter written to Philip D'Arcy Hart at the Medical
Research Council Laboratories in London and dated July 29th 1968, Snow himself
said that “We have revived some interest in this topic after a lapse of a number of
years”. This would suggest that the project had been completely abandoned in the
late 1950s and early 1960s. Sometime then in the 1960s, interest in mycobactins
must have then re-started but, in all probability, only Alan Snow, with possibly just
one or two technical assistants, would have been engaged on the project for most
of the remainder of the program.