360 PHOTOMECHANICAL CONSIDERATIONS 



points of attachment to the cristae and, indeed, this appears to be 

 consistent with one interpretation of the electron micrographic data 

 (7). 



Effect of glycerol upon the kinetics of light-induced cytochrome oxida- 

 tion in Chromatium, 



Encouraged by the striking effects of glycerol upon electron trans- 

 port in the cytochrome chain, we have extended these experiments to 

 studies of light-induced reactions in suspensions of photosynthetic 

 bacteria. The experimental procedure is indicated in Fig. 2, which in- 

 dicates the time course of light-induced cytochrome oxidation in sus- 

 pensions oiChromatium. A measuring wavelength of 422 m// and a ref- 

 erence wavelength of 460 van are employed (4), Anaerobiosis has pre- 

 viously been established in the bacterial suspension and illumination 

 with infrared light (88 A filter, 400 Lux) causes an abrupt oxidation 

 of the cytochrome component of the bacteria which is half complete 

 in approximately 0.2 seconds. Independent controls indicate that the 

 time for half-maximal illumination of the sample is approximately 

 0.03 seconds. The response time of the amplifier is also more rapid 

 than the absorbancy changes. Thus, the upward slope of the trace is 

 limited by the rate of chlorophyll activation and electron transfer be- 

 tween cytochrome and chlorophyll. As is characteristic of the light- 

 induced phenomena, the rapid phase is followed by a slow phase and, 

 after two seconds of illumination, the light is turned off in the same 

 short time interval as it was turned on. The trace deflects downward 

 in a half-time comparable to that observed upon turning on the light. 



Isec h- -H Isec 



Chromatium + 25° C 422-460m/i Chromatium In 67% Glycerol + 25° C 



Anaerobic Light Response Anaerobic Light Response 



^ '^L^^^^O^t /aA=0.02-J 



Fig. 2. An illustration of the experimental technique used in evaluating 

 the rates of light-induced cytochrome oxidation in suspensions of Cliro- 

 luotiioii. The kinetics arc measured by means of the double-beam spectro- 

 photometer, employing infrared illumination of the sample. The record 

 on the left represents the reaction kinetics in the absence of glycerol and, 

 on the right, in the presence of 67 per cent glycerol. An absorbancy de- 

 crease at 422 m/i relative to 460 mfi is indicated by an upward deflection 

 of the trace (HS-19), 



