5-Formyltetrahydrofolate polyglutamates are slow tight binding inhibitors of serine hydroxymethyltransferase.
The interaction of the mono- and triglutamate forms of 5-methyltetrahydrofolate and 5-formyltetrahydrofolate with serine hydroxymethyltransferase were determined by several methods. These methods included: determining dissociation constants by observing the absorbance at 502 nm of a ternary complex of the enzyme, glycine, and the folate compounds; determining inhibition constants from steady-state reactions; and determining the rate of formation and breakdown of the enzyme inhibitor complex by rapid reaction kinetics. Studies of the dissociation and inhibitor constants showed that both 5-methyltetrahydrofolate and 5-formyltetrahydrofolate have essentially the same affinity for the enzyme-glycine binary complex. However, rapid reaction and steady-state kinetic studies showed that the triglutamate form of 5-formyltetrahydrofolate both binds and is released much more slowly from the enzyme-glycine binary complex, compared with the triglutamate form of 5-methyltetrahydrofolate. The results also showed that only one rotamer of 5-formyltetrahydrofolate binds at the active site of serine hydroxymethyltransferase. The results are discussed in terms of the possible role of 5-formyltetrahydrofolate polyglutamates in regulation of one-carbon metabolism.
Stover
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Department of Biochemistry and Molecular Biophysics, Virginia Commonwealth University, Medical College of Virginia, Richmond 23298.
Schirch
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D000818:Animals; D002942:Circular Dichroism; D003600:Cytosol / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D005998:Glycine / Q000378:metabolism; D012696:Glycine Hydroxymethyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D015394:Molecular Structure; D011485:Protein Binding; D011624:Pteroylpolyglutamic Acids / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits; D013329:Structure-Activity Relationship
D011624:Pteroylpolyglutamic Acids; D012696:Glycine Hydroxymethyltransferase; D005998:Glycine