Alkyl isocyanides serve as transition state analogues for ligand entry and exit in myoglobinn

The pathways identified by alkyl isocyanides (CNRs) for diatomic ligand movement into and out of Mb, with their side chains acting as transition state analogues are reviewed. The strong correlation observed between the fraction of in conformer, [F.sub.in], for long-chain MbCNR complexes, the fraction of geminate recombination of photodissociated [O.sub.2], and the bimolecular rates of [O.sub.2] entry into the distal pocket revealed that alkyl isocyanides serve as transition state analogues for the movement of [O.sub.2] into and out of the binding pocket of Mb.