Molecular Science for Elucidation of Proton Active Transport and Electron Transfers through Proteins.

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Active transport of protons by proteins is presumably based on pKa changes of some proton-carrying residues upon conformation change. In order to examine protonation-dependent protein dynamics, time-resolved ultraviolet resonance Raman spectra were pursued for the quaternary structure change of hemoglobin (Hb) from R to T upon photodissociation of its carbonmonoxide adduct. Raman spectra were probed by laser pulses at 218nm with 10ns width, while CO was photodissociated by another laser pulses at 416nm with lons width. The delay time of the probe pulse from the pump pulse was varied from -200mus to 500mus. The relative intensity of a tryptophane band at 1011cm^<-1> to a phenylalanine band at 1003cm^<-1> changed with the quaternary structure change. The change took place at 5 - 20mus after photolysis at pH7.4 but it had been completed at lOmus after photolysis at pH5.8 where Bohr residues are protonated. We deduced the tryptophane residue responsible for the Raman spectral change is beta37-Trp and discussed a mechanism by which a structural change of heme in alpha subunit is communicated to the beta subunit.We also investigated reaction intermediates of cytochrome oxidase by using time-resolved resonance Raman spectroscopy and proposed likely structures of partially reduced oxygen. The results are published separately.