Combination of potentiometry and resonance Raman spectroscopy for the analysis of a redox protein

This paper describes apparatus and procedures for combining resonance Raman and optical absorption spectroscopies with potentiometry for the study of redox-active heme proteins. A specially designed anaerobic titration cell is described which allows for the laser excitation of the sample and the monitoring of both Raman scattered light and directly transmitted light from an optical source. New procedures for utilization of A/D and D/A converters on a standard I/O computer card are described, which allow for computer-controlled potentiometry and coulometry. The system was tested with cytochrome c, a well-characterized respiratory protein. The correct values for the midpoint potential and electron number of the Nernst equation were obtained both by the optical absorption and resonance Raman measurements.