Circular dichroism studies in the near UV of ligand binding to chicken liver dihydrofolate reductase.

Circular dichroism spectra in the near UV (250-400 nm) were recorded for chicken liver dihydrofolate reductase and its complexes with substrates, inhibitor methotrexate, and cofactor NADPH. The spectra obtained with methotrexate are very like those published for bacterial dihydrofolate reductases. Thus we suggest that the conformations of methotrexate at the active site of the chicken liver enzyme and that of the enzyme from Lactobacillus casei which has been described extensively in X-ray studies show a great similarity. The same similarity does not hold in the case of the substrate dihydrofolate where the C.D. spectra of binary complexes obtained with enzymes from different sources are different.