JBC, Vol. 254, Issue 24, 12285-12288, Dec, 1979
Thymidylate synthetase and 2'-deoxyuridylate form a tight complex in the presence of pteroyltriglutamate
A. Lockshin and P. V. Danenberg
Thymidylate synthetases of human and bacterial origin form a tightly bound
complex with the substrate dUMP in the presence of pteroyltriglutamate.
This complex and the weaker enzyme . dUMP binary complex can be isolated
and conveniently assayed by nitrocellulose disc filtration using [6-3H]dUMP
as the radioactive ligand. Intact thymidylate synthetase . dUMP .
pteroyltriglutamate complex can be obtained by gel filtration
chromatography on Sephadex G-25, but the binary enzyme . dUMP complex
dissociates under the same conditions. Scatchard plots show the presence of
two nonequivalent dUMP binding sites on the enzyme for the
pteroyltriglutamate complex, with dissociation constants of 5 and 95 nM
compared to 730 nM for the binary complex. The implications of these
findings for folate analog inhibition of thymidylate synthetase are
discussed.