Biosynthesis of riboflavin. Studies on the mechanism of L-3,4-dihydroxy-2-butanone 4-phosphate synthase.
The riboflavin precursor, L-3,4-dihydroxy-2-butanone 4-phosphate, is formed from D-ribulose 5-phosphate by a single 24-kDa enzyme. Studies with various specifically 13C-labeled D-ribulose 5-phosphates as substrate showed that the carbon atoms 1-3 of the enzyme product correspond to carbon atoms 1-3 of the substrate, whereas C-4 of the product stems from C-5 of the substrate. Carbon atom 4 of the substrate is released as formate together with the hydrogen atom attached to it. The skeletal rearrangement which leads to the loss of C-4 and the direct linkage between C-3 and C-5 of the substrate is an intramolecular reaction. The hydrogen atom at C-3 of the enzyme product is introduced from solvent water. A reaction mechanism which is in agreement with all experimental data is proposed.
Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Federal Republic of Germany.
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Volk
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Bacher
D002175:Candida / Q000201:enzymology; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D004798:Enzymes / Q000378:metabolism*; D019751:Intramolecular Transferases; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D012256:Riboflavin / Q000096:biosynthesis*; D012274:Ribulosephosphates / Q000378:metabolism; D013403:Sugar Phosphates / Q000096:biosynthesis*
D004798:Enzymes; D012274:Ribulosephosphates; D013403:Sugar Phosphates; C066494:3,4-dihydroxy-2-butanone-4-phosphate; C031524:ribulose 5-phosphate; D002238:Carbohydrate Epimerases; D019751:Intramolecular Transferases; C066493:L-3,4-dihydroxy-2-butanone-4-phosphate synthase; D012256:Riboflavin