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Figure 1.
(a) Overall bacterial pathway. AIR (12) is converted to HMP-P
(15) by HMP-P synthase (ThiC), which is phosphorylated by ThiD
to give HMP pyrophosphate (3). The thiazole moiety (2) is
biosynthesized from DXP (6), cysteine (8) and dehydroglycine
(34). The dehydroglycine is generated from glycine (ThiO) in B.
subtilis and from tyrosine (ThiH) in E. coli. The pyrimidine and
thiazole are coupled by ThiE to give thiamine phosphate (4), and
ThiL catalyzes the final phosphorylation. (b) Conversion of AIR
to the thiamine pyrimidine in bacteria and plants. The color
coding indicates the source of nonhydrogen atoms in HMP-P as
demonstrated by labeling studies. (c) Biosynthesis of thiamine
pyrimidine in fungi. In fungi the pyrimidine moiety is derived
from histidine (13) and pyridoxal 5'-phosphate (14) using a
single enzyme, THI5p. The color coding indicates the source of
nonhydrogen atoms. (d) The HMP-P synthase reactions. When
iron-sulfur cluster–loaded HMP-P synthase is reduced with
dithionite, it reduces SAM (16) to generate methionine (28) and
the 5'-deoxyadenosyl (5-dAdo) radical (17), which is required by
HMP-P synthase to convert AIR to HMP-P.
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