Conformational disorder of the distal leucine in monomeric Glycera hemoglobins and implications for oxygen binding.

1H NMR studies of the carbon monoxide complexes of the major monomeric hemoglobins from Glycera dibranchiata show that distal leucine is conserved at position E7. The observed ring current shifts and nuclear Overhauser enhancements indicate conformational disorder of the leucine E7 side chain. The conformational substates interconvert rapidly on the NMR time scale. The rapid conformational fluctuations of leucine E7 may play a fundamental role in governing diffusion of ligands to the heme.