title: Evidence for the accumulation of a stable intermediate in the nonenzymatic hydrolysis of 5,10-methenyltetrahydropteroylglutamate to 5-formyltetrahydropteroylglutamate.
abstract: Solutions of 5,10-methenyltetrahydropteroylglutamate can be converted to a stable hydrated adduct by heating solutions at 50 degrees C at pH values of 3-5 for several hours. The adduct is stable at pH values from 4 to 9 for hours, but at pH values below 2 it is converted to 5,10-methenyltetrahydropteroylglutamate and at pH values above 8 it is converted to 5-formyltetrahydropteroylglutamate. Arguments are presented that the adduct is (11R)-5,10-hydroxymethylenetetrahydropteroylglutamate formed from (11S)-5,10-hydroxymethylenetetrahydropteroylglutamate by formation of an ylide at C-11 which undergoes inversion of the electron pair to form the (11R) isomer. The (11R) hydrated adducted is believed to be the isomer of 5,10-methenyltetrahydropteroylglutamate referred to as anhydroleucovorin B by Cosulich et al. [Cosulich, D. C., Roth, B., Smith, J. M., Hultquist, M. E., & Parker, R. P. (1952) J. Am. Chem. Soc. 74, 3252-3263]. In addition, a new mechanism for the formation of 5-formyltetrahydropteroylglutamate from either 5,10-methenyltetrahydropteroylglutamate or 10-formyltetrahydropteroylglutamate via (11R)-5,10-hydroxymethylenetetrahydropteroylglutamate is proposed. A requirement for this pathway is that the formyl proton of 10-formyltetrahydropteroylglutamate exchange with solvent protons. The exchange of this formyl proton was observed at all pH values from 5.5 to 11.5 at a rate which exceeded by more than an order of magnitude the rate of formation of 5-formyltetrahydropteroylglutamate.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Virginia Commonwealth University, Richmond 23298.
authors.forename: P
authors.initials: P
authors.lastname: Stover
authors.forename: V
authors.initials: V
authors.lastname: Schirch
mesh_terms: D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D002955:Leucovorin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013763:Tetrahydrofolates / Q000737:chemistry*
chemical_list: D013763:Tetrahydrofolates; C018092:5,10-methenyltetrahydrofolate; D002955:Leucovorin