NEAR-INFRARED SPECTRAL CHANGES OF CYTOCHROME AA(3) DURING POTENTIOMETRIC TITRATIONS

Singular value decomposition (SVD) was used to deconvolute the spectra l changes occurring in the near infrared region during potentiometric titrations of cytochrome aa(3). Overall oxidized minus reduced differe nce spectra revealed a broad absorbance feature centered near 830 nm w ith an apparent E(m) near 250 mV. However, SVD did not isolate any spe ctral species with an absorbance centered near 830 nm. it was found th at the spectral changes occurring in the wavelength region from 650 to 950 nm were associated mainly with cytochromes a and a(3). It was con cluded that the absorbance at 830 nm should not be used as an independ ent measure of the concentration of Cu-A in cytochrome aa(3).