Thiamine vitamin biosynthesis

Figure 4 Biosynthesis of thiamine (vitamin ). 37, aminoimidazole ribotide 38, 2-methyl-4-amino-5-hydroxymethyl-pyrimidine phosphate 39, pyridoxal 5 -phosphate 40, histidine 41, 2-methyl-4-amino-5-hydroxymethyl-pyrimidine pyrophosphate 42, 4-methyl-5-p-hydroxyethylthiazole phosphate 43,1 -deoxy-D-xylulose 5-phosphate 44, 5-ADP-D-ribulose 45, thiamine phosphate 46, thiamine pyrophosphate.

Anaerobic pathway of vitamin biosynthesis 98H(47)1051. Biosynthesis of thiamine 97AG(E)1032. 

Pyrimidine biosynthesis, de novo pyrimidine biosynthesis total synthesis of the pyrimidine ring of uracil, thymine, cytosine and their derivatives from carbamoyl phosphate and aspartate in all living cells. The pyrimidine ring of thiamin (vitamin Bj) has a different biosynthetic origin (see below). 

Biosynthesis of the pyrimidine ring of thiamin (vitamin Bi) from aminoimidazoleribonucleotide. The 2-methyl-4-amino-5-hydroxymethyl-pyrimidine ring present in thiamin is synthesized from aminoimida-zoleribomlcleotide, which is an intermediate in purine biosynthesis (Fig. 4). 

Thyroxine affects vitamin metabolism by interfering with the requirement of a vitamin and interfering with vitamin biosynthesis. The requirements for thiamine and riboflavin, two vitamins involved in the cell s... 

The vitamin thiamine may not at first sight have a close relation to carbohydrates, but David and Estramareix (Paris) trace here a remarkable story in the elucidation of its biosynthesis. Quite different pathways are shown to exist in... 

Except for some vitamin B12-dependent reactions, the cleavage or formation of carbon-carbon bonds usually depends upon the participation of carbonyl groups. For this reason, carbonyl groups have a central mechanistic role in biosynthesis. The activation of hydrogen atoms (3 to carbonyl groups permits (3 condensations to occur during biosynthesis. Aldol or Claisen condensations require the participation of two carbonyl compounds. Carbonyl compounds are also essential to thiamin diphosphate-dependent condensations and the aldehyde pyridoxal phosphate is needed for most C-C bond cleavage or formation within amino acids. 

Figure 22-2 The glyceraldehyde 3-phosphate pyruvate alternative pathway of isoprenoid biosynthesis. The intermediate 1-deoxyxylulose 5-phosphate may enter terpenes, vitamin B6, and thiamin. Isopentenyl diphosphate is shown as the final product, but the intermediate steps are uncertain. See Lange et al 2 ...

In bacteria, the pyrimidine precursor 38 is derived from 5-aminoimidazole ribotide (37), an intermediate of the basic branch of purine biosynthesis, which supplies all carbon atoms for 38 by a complex rearrangement reaction (the fate of the individual carbon atoms is indicated by Greek letters in Fig. 4). In yeasts, a totally unrelated reaction sequence uses carbon atoms from vitamin Be (39) that are indicated by roman letters in Fig. 4 for the assembly of the thiamine precursor 38,... 

Some coenzymes serve as biosynthetic precursors that afford structural parts of other coenzymes. Thus, the benzenoid moiety of the flavocoenzyme FMN serves as a precursor for the lower ligand 26 of the central cobalt ion in vitamin B12 (20) (Fig. 3) (5). Pyridoxal and NAD are used as precursors for the biosynthesis of thiamine in yeast (Fig. 4) (23, 24). 

Branching of pathways is relevant in several cases. Thus, intermediates of the porphyrin biosynthetic pathway serve as precursors for chlorophyll (17, Fig. 2) and for the corrinoid ring systems of vitamin B12 (20, Fig. 2) (17). 1-Deoxy-D-xylulose 5-phosphate (43) serves as an intermediate for the biosynthesis of pyridoxal 5 -phosphate (39, Fig. 5), for the terpenoid precursor IPP (86) via the nonmevalonate pathway (Fig. 11), and for the thiazole moiety of thiamine pyrophosphate (46, Fig. 4). 7,8-Dihydroneopterin triphosphate (29, Fig. 3) serves as intermediate in the biosynthetic pathways of tetrahydrofolate (33) and tetrahydrobiopterin (31). The closely related compound 7,8-dihydroneopterin 2, 3 -cyclic phosphate is the precursor of the archaeal cofactor, tetrahydromethanopterin (34) (58). A common pyrimidine-type intermediate (23) serves as precursor for flavin and deazaflavin coenzymes. Various sulfur-containing coenzymes (thiamine (9), lipoic acid (7), biotin (6), Fig. 1) use a pyrosulfide protein precursor that is also used for the biosynthesis of inorganic sulfide as a precursor for iron/sulfur clusters (12). 

Another example of the biosynthesis of a thiazole ring is in enzymatic biosynthesis of thiamin. Thiamin is a thiazole-containing vitamin whose supply in humans relies on diet. It acts as a coenzyme and plays an important role in carbohydrate and amino acid metabolism <2003NPR184>. Thiamin deficiency can be fatal. 

Some of the vitamins in the coeiizymc form associate tightly wdth specific enzymes, but not via a covalent linkage. Immediately after biosynthesis on the ribosome, enzymes do itot contain their cofactor, and these are called apoenzymes. An eitzyme containing its required cofactor is called a hoLoenzyme, With removal of the cofactor, the enzyme is also called an apoenzyme. The enzymes that exist in apoenzyme and holoenzyme forms include those that use vitamin Bx2, vitamin B, thiamin, and riboflavin-based cofactors. Enzymes that use niacin-based cofactors, folate, ascorbate, and vitamin K are not said to exist in apoenzyme and holocn-zyme forms. These enzymes bind their cofactors relatively weakly, and the cofactors behave in a manner similar to substrates. 

Vitamin Bi is an essential co-factor for several enzymes of carbohydrate metabolism such as transketolase, pyruvate dehydrogenase (PDH), pyruvate decarboxylase and a-ketoglutarate dehydrogenase. To become the active co-factor thiamin pyrophosphate (TPP), thiamin has to be salvaged by thiamin pyrophosphokinase or synthesized de novo. In Escherichia coli and Saccharomyces cerevisiae thiamin biosynthesis proceeds via two branches that have to be combined. In the pyrimidine branch, 4-amino-5-hydroxymethy-2-methylpyrimidine (PIMP) is phosphorylated to 4-amino-2-methyl-5-hydroxymethyl pyrimidine diphosphate (PIMP-PP) by the enzyme HMP/HMP-P kinase (ThiD) however, the step can also be catalyzed by pyridoxine kinase (PdxK), an enzyme also responsible for the activation of vitamin B6 (see below). The second precursor of thiamin biosynthesis, 5-(2-hydroxyethyl)-4-methylthiazole (THZ), is activated by THZ kinase (ThiM) to 4-methyl-5-(2-phosphoethyl)-thiazole (THZ-P), and then the thia-zole and pyrimidine moieties, HMP-PP and THZ-P, are combined to form thiamin phosphate (ThiP) by thiamin phosphate synthase (ThiE). The final step, pyrophosphorylation, yields TPP and is carried out by thiamin pyrophosphorylase (TPK). 

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