A new measurement system for UV resonance Raman spectra of large proteins and its application to cytochrome c oxidase

A new type of ultraviolet resonance Raman (UVRR) measurement system suitabl e to a limited amount of large protein samples is proposed and the results from its application to bovine cytochrome c oxidase (CcO) is presented. To minimize the sample damage caused by high-flux UV laser illumination and to reject visible fluorescence from the sample, frequency-doubling of a mode- locked Ar+ ion laser and a solar blind multichannel detector were employed, respectively. A new spinning cell was designed so that the sample solution could be stirred during spinning of the cell. Combination of all these dev ices resulted in successful observation of high quality UVRR spectra of CcO excited at 244 nm. The RR bands of tryptophan and tyrosine residues domina ted the observed spectra, while an extra band appeared at 1656 cm(-1). The frequency of the extra band as well as those of all other bands were unalte red by the redox change of metal centers and ligand binding to heme a(3). D eprotonation of a tyrosine residue(s) with a low pK(a) value was detected f or the resting state at pH 9.1. Examination of all possible assignments led us to conclude that the extra band arose from the linoleoyl side chain of phospholipids and its intensity suggested the presence of 21 linoleoyl grou ps per CcO molecule.