Thiamine orthophosphate

This thiamin pyrophosphate-dependent enzyme [EC 4.1.2.9] catalyzes the reaction of D-xylulose 5-phosphate with orthophosphate to produce acetyl phosphate, d-glyceraldehyde 3-phosphate, and water. 

This enzyme [EC 1.2.3.3], which requires thiamin pyrophosphate and FAD, catalyzes the reaction of pyruvate with orthophosphate, dioxygen, and water to produce acetyl phosphate, carbon dioxide, and hydrogen peroxide. 

Nucleoside triphosphatase [Unspecific diphosphate phosphohydrolase] (3.6.1.15) is produced and catalyzes the reaction NTP + H2O = NDP + orthophosphate. [Also hydrolyses other nucleoside triphosphates, diphosphate, thiamin diphosphate and FAD.] m7G (5 ) pppN pyrophosphatase [7-Methylguanosine,... 

Recently, the mechanism has been estabhshed by which this union of the two fragments is achieved by cell-free extracts of baker s yeast Saccharo-myces ccrevisiae) -. It proceeds according to the diagram shown in Fig. i. 2-Methyl-4-amino-5-hydroxymethylpyrimidine (Pm) is enzymically phos-phorylated in position 7 by ATP in the presence of Mg2+ ions, to form the pyrophosphate derivative. The thiazole part (Th) is similarly phosphorylated (in the aliphatic side chain), but in this case the monophosphate derivative is formed. Both intermediates are hnked together by a third enzyme, and pjrrophosphate (or possibly two successive orthophosphate molecules) is split off. The primarily formed thiamine monophosphate is dephosphorylated bj a phosphatase. Enzyme (i) has been separated from enzymes (2) and (3). 

TPP is inactivated by treatment with 1 N hydrochloric acid at 100° for 15 min. owing to the hydrolysis of the pyrophosphate linkage and yields orthophosphate and thiamine monophosphate. Treatment of TPP with alkali splits off pyrophosphate and gives free thiamine. TPP, like thiamine,... 

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