[Comparative topography of the catalytic sites of chromosomal dihydrofolate reductases and that of the enzyme encoded in R 67 plasmid from E. coli].

The trimethoprim-resistant dihydrofolate reductase specified in E. coli by plasmid R 67, when compared, with other enzymes catalyzing the same reaction, to have a dissimilar primary, secondary, tertiary and quaternary structure. In regard to the tertiary structure, we show here that the pteridine binding site, in the plasmid-encoded enzyme, has a geometrical similarity with that of other chromosomal specified reductases.