| X-RAY DIFFRACTION |
8.00 |
277 |
THE TERNARY COMPLEX OF DHFR WITH NADPH AND 39B WAS FORMED BY MIXING HUMAN DHFR (20 MG/ML IN 25 MM KPO4 (PH 7.0), 0.1 MM EDTA, AND 3 MM NAN3) WITH 60 MM NADPH, FOLLOWED 15 MINUTES LATER BY 60 MM OF INHIBITOR IN DMSO (FINAL CONCENTRATIONS OF 2 MM NADPH AND 2 MM INHIBITOR). THIS COMPLEX SOLUTION WAS MIXED WITH AN EQUAL VOLUME OF PRECIPITANT CONTAINING 24-33% PEG 4000, 0.2 M LI2SO4, 0.1 M TRIS CL (PH 7.9-8.4), 5% GLYCEROL, AND EQUILIBRATED WITH THE PRECIPITANT BY HANGING DROP VAPOR DIFFUSION AT 277 K. THE CRYSTAL GREW IN ABOUT 3 WEEKS. THE CRYSTAL WAS FLASH-COOLED DIRECTLY IN LIQUID NITROGEN AFTER HARVESTING INTO MOTHER LIQUOR CONTAINING 10% GLYCEROL. NOTE THAT THE INHIBITOR IS ACTUALLY A RACEMIC MIXTURE OF 39B AND ITS ENANTIOMER, HERE CALLED 39E. IT IS THE RACEMATE THAT IS BOUND IN THE CRYSTAL, REPRESENTED IN THE COORDINATES AS A 1:1 STATISTICALLY-DISORDERED MIXTURE OF 39B AND 39E. |
