title: Substrate specificity of mammalian folylpoly-gamma-glutamate synthetase for 5,8-dideazafolates and 5,8-dideaza analogues of aminopterin.
abstract: The substrate specificity of pig liver folylpolyglutamate synthetase (tetrahydrofolate:L-glutamate gamma-ligase (ADP-forming), EC 6.3.2.17) for classical 5,8-dideaza analogues of folic acid, isofolic acid aminopterin and isoaminopterin has been investigated. 5,8-Dideazafolate and 5,8-dideazaaminopterin are very effective substrates with activities approaching those of the best reduced folate substrates. The analogous isofolate analogues are less effective substrates, but still better than folic acid. The 5-chloro substituent is the only modification that consistently increases the on rate, with 5-chloro-5,8-dideazaaminopterin being the most effective substrate found, thus far, for the enzyme. Methylation at positions 9 or 10 generally decreases binding, while 5-methylation increases the binding of 4-oxoquinazolines, but decreases the binding of their 4-amino counterparts. The presence of a formyl group at N9 or N10 has the opposite effect, decreasing the binding of 4-oxo analogues while increasing the rate for 4-amino derivatives. Increases in on rate with methyl, formyl or 4-amino substitutions are only significant when the parent compound is a poor substrate, suggesting that these groups do not interact directly with the enzyme but cause conformational changes in the structure of the substrate that influence binding to the enzyme.
authors.affiliation: Department of Nutritional Sciences, University of California, Berkeley 94720.
authors.forename: D J
authors.initials: DJ
authors.lastname: Cichowicz
authors.forename: J B
authors.initials: JB
authors.lastname: Hynes
authors.forename: B
authors.initials: B
authors.lastname: Shane
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000630:Aminopterin / Q000031:analogs & derivatives* / Q000378:metabolism*; D000818:Animals; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D007700:Kinetics; D015394:Molecular Structure; D010453:Peptide Synthases / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013552:Swine
chemical_list: D005971:Glutamates; D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D005492:Folic Acid; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase; D000630:Aminopterin