Probable binding region of small hydrophobic molecules on hemoglobin. Spin label-induced nuclear magnetic relaxation

The interactions of phenylalanine, valine and alanine with hemoglobin have been compared using spin lattice nuclear magnetic relaxation and spin label-enhanced nuclear magnetic relaxation measurements. The results indicate that phenylalanine exhibits weak hydrophobic binding to hemoglobin, and that the binding site is probably located within about 7-13 A of the nitroxide free electron of spin-labeled hemoglobin. This distance is consistent with the binding site being located within a hydrophobic region comprised of the side chains of the beta-chain residues, phenylalanine beta 85, leucine beta 88 and leucine beta 91, and perhaps a segment of the beta heme porphyrin ring.