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

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