In anaerobic organisms such as E. coli the tyrosine lyase ThiH is essential for the biosynthesis of the thiazole moiety of the vitamin thiamine. ThiH is a member of the “radical AdoMet” family. The products formed by cleavage of tyrosine in vitro have been identified and suggest a radical‐mediated cleavage resulting in p‐cresol and dehydroglycine which is hydrolyzed to glyoxylate.

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If vaccination is to precede the adolescent rise in MenB carriage, these data suggest it should take place in early adolescence. Studies assessing vaccine impact should use molecular methods to detect carriage.

Thiamine is biosynthesized by combining two heterocyclic precursors. In Escherichia coli and other anaerobes, one of the heterocycles, 4-methyl-5-(␤-hydroxyethyl) thiazole phosphate, is biosynthesized from 1-deoxyxylulose-5-phosphate, tyrosine, and cysteine. Genetic evidence has identified thiH, thiG, thiS, and thiF as essential for thiazole biosynthesis in E. coli. In this paper, we describe the measurement of the thiazole phosphateforming reaction using purified protein components. The activity is shown to require four proteins isolated as heterodimers: ThiGH and ThiFS. Reconstitution of the [4Fe-4S] cluster in ThiH was essential for activity, as was the use of ThiS in the thiocarboxylate form. Spectroscopic studies with ThiGH strongly suggested that S-adenosylmethionine (AdoMet) bound to the [4Fe-4S] cluster, which became more susceptible to reduction to the ؉1 state. Assays of thiazole phosphate formation showed that, in addition to the proteins, Dxp, tyrosine, AdoMet, and a reductant were required. The analysis showed that no more than 1 mol eq of thiazole phosphate was formed per ThiGH. Furthermore, for each mole of thiazole-P formed, 1 eq of AdoMet and 1 eq of tyrosine were utilized, and 1 eq of 5-deoxyadenosine was produced. These results demonstrate that ThiH is a member of the "radical-AdoMet" family and support a mechanistic hypothesis in which AdoMet is reductively cleaved to yield a highly reactive 5-deoxyadenosyl radical. This radical is proposed to abstract the phenolic hydrogen atom from tyrosine, and the resultant substrate radical cleaves to yield dehydroglycine, which is required by ThiG for the thiazole cyclization reaction.Thiamine (vitamin B 1 ) is a key nutrient for humans with a recommended daily dose of 1.4 mg, and a deficiency of thiamine causes the disease beriberi (1). Thiamine pyrophosphate (TPP) 3 is an essential cofactor for several enzymes involved in carbohydrate and amino acid metabolism, including transketolase, pyruvate dehydrogenase, and ␣-ketoglutarate dehydrogenase (2, 3). Although studied for many years, the biosynthetic steps leading to TPP are not fully understood. Thiamine phosphate (TP) (Fig. 1, 6) is formed by ThiE, an enzyme that covalently links two independently formed heterocyclic precursors, 4-amino-5-hydroxymethylpyrimidine-pyrophosphate (Fig. 1, 5, Hmp-PP) and 4-methyl-5-(␤-hydroxyethyl)-thiazole phosphate (Thz-P) (Fig. 1, 4). This is converted to TPP by a ThiLdependent phosphorylation reaction (4, 5). 4-Amino-5-hydroxymethylpyrimidine phosphate is formed by a complex rearrangement of 5-aminoimidazole ribotide by ThiC (6), which upon phosphorylation by ThiD results in 4-amino-5-hydroxymethylpyrimidine-pyrophosphate (6, 7).The synthesis of Thz-P has been studied in a number of prokaryotes, most notably in the facultative anaerobes Escherichia coli and Salmonella sp., the aerobe Bacillus subtilis, and the eukaryote Saccharomyces cerevisiae (8, 9). Whole cell feeding studies in E. coli and knock-out mutants thereof indicated that Thz-P synthesis is dependent on th...