Oxidation of Cytochromes upon Near- Infrared 

 Irradiation of Chromatium 



JOHN M. OLSON,* Johnson Research Foundation, University of Pennsyl- 

 vania, Philadelphia, Pennsylvania 



The first observation of the oxidation of cytochromes in photo- 

 synthetic bacteria upon illumination was made by Duysens (1) 

 in his studies of absorption spectrum changes in Rhodo spirillum 

 ruhrum. Subsequently, Chance and Smith (2) confirmed and rein- 

 interpreted Duysens' observation with a more detailed study of the 

 cytochromes involved. My observations were made on the photo- 

 synthetic sulfur bacterium, Chromatium D, furnished by Dr. M. D. 

 Kamen. 



The bacteria were cultured at 29 °C. in an inorganic medium con- 

 taining sodium sulfide, sodium thiosulfate, and sodium bicarbonate 

 as substrates. Glass-stoppered culture bottles were illuminated by 

 tungsten lamps. In each experiment on the effects of illumination a 

 concentrated suspension of bacteria in growth medium was observed 

 by means of a double-beam spectrophotometer (3). The sample 

 could be irradiated by a near-infrared beam (X > 700 m^u) perpendic- 

 ular to the measuring beams. In other experiments two samples in 

 the dark were compared in a recording spectrophotometer (4). 

 All experiments were performed at room temperature (23° to 27 °C.). 



Since the suspensions were aerobic after the centrifugation and 

 resuspension necessary for concentrating the bacteria, some sus- 

 pensions were covered with paraffin oil to obtain anaerobic samples. 

 After 15 to 60 minutes under oil in the dark the absorption of a sam- 

 ple at 422 m/z slowly increased to a new steady-state value. The sam- 

 ple was known to be anaerobic when irradiation caused a large 

 diphasic decrease in absorption (Fig. 1) in contrast to the small 

 monophasic decrease in absorption characteristic of aerobic samples. 



The change in absorption spectrum of anaerobic suspensions upon 

 irradiation for about 3 minutes is given by curve A in Fig. 2. This 

 difference spectrum has an alpha peak, a beta peak, and a gamma 



* National Science Foundation Predoctoral Fellow. 



174 



