Open AccessBiosynthesis of vitamin B 2
Author(s) -
Kaiser Johannes,
Schramek Nicholas,
Eberhardt Sabine,
Püttmer Stefanie,
Schuster Michael,
Bacher Adelbert
Publication year - 2002
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2002.03239.x
Subject(s) - formate , chemistry , pyrophosphate , gtp' , stereochemistry , cysteine , biosynthesis , hydrolysis , serine , histidine , enzyme , biochemistry , catalysis
GTP cyclohydrolase II catalyzes the hydrolytic release of formate and pyrophosphate from GTP producing 2,5‐diamino‐6‐ribosylamino‐4(3 H )‐pyrimidinone 5′‐phosphate, the first committed intermediate in the biosynthesis of riboflavin. The enzyme was shown to contain one zinc ion per subunit. Replacement of cysteine residue 54, 65 or 67 with serine resulted in proteins devoid of bound zinc and unable to release formate from the imidazole ring of GTP or from the intermediate analog, 2‐amino‐5‐formylamino‐6‐ribosylamino‐4(3 H )‐pyrimidinone 5′‐triphosphate. However, the mutant proteins retained the capacity to release pyrophosphate from GTP and from the formamide‐type intermediate analog. The data suggest that the enzyme catalyzes an ordered reaction in which the hydrolytic release of pyrophosphate precedes the hydrolytic attack of the imidazole ring. Ring opening and formate release are both dependent on a zinc ion acting as a Lewis acid, which activates the two water molecules involved in the sequential hydrolysis of two carbon–nitrogen bonds.