Energy Transfer and Conservation in the Respiratory Chain 601 



protein and thence to adjacent carriers seems unlikely in view of more 

 accurate data on the photochemical action spectrum (Castor and Chance, 

 1955) and recent studies of photodissociation spectra in the visible region 

 (cf. Chance and Spencer, 1959). It is very unlikely that there exist bands in 

 the photochemical action spectrum that correspond accurately to the a-bands 

 of cytochromes b or c, and the actual positions of the 'anomalous' bands 

 supports this view (Keilin and Hartree, 1953). In summary, the transfer of 

 electronic energy between the carriers of the respiratory chain by a resonance 

 mechanism appears unlikely, due to the peculiar property of the haem itself 

 to act as a trap for such energy, and such a process does not contribute 

 measurably to energy transfer in respiratory activity of the cytochrome chain. 

 Tliis conclusion is in agreement with the previously mentioned studies of 

 Hagins and Jennings (1959) on retinal rods. They find no system for trans- 

 ferring electronic excitation over distances comparable to the dimensions of 

 the rods. 



Ch lorophyll-cyto chrome In ter act ions 



The photosynthetic purple sulphur bacterium, Chromatium, strain D, 

 shows high efficiency in the transfer of oxidizing equivalents from bacterial 

 chlorophyll to cytochrome (■~2 quanta/electron (Olson, 1958)). In fact, there 

 appears to be an earlier transfer of oxidizing equivalents to cytochrome than 

 of reducing equivalents to pyridine nucleotide (Chance and Olson, 1960). 



The eff'ect of temperature upon the light response is small in R. rubrum 

 (Chance, 1957) and Chromatium (Olson, 1958). Recent investigations of 

 Chromatium over a wide range of temperatures, including measurements of 

 frozen bacteria (Chance and Nishimura, 1960), show the rate of the light- 

 induced oxidation to be the same within the accuracy of the experimental 

 data at +28° and — 22°C. An example of this type of studyis afforded by Fig. 1. 

 Here the double-beam spectrophotometer is used to record a decrease of 

 absorbancy at 423 m^* (measured with respect to 460 m/^) caused by infra-red 

 illumination of the suspension of bacteria. With the sample at room tem- 

 perature, illumination at the point 'on' causes oxidation of 'cytochrome 423' 

 at a rate of 0-13 /^moles of Fe 1.-^ sec-^ (for the assumptions involved in the 

 extinction coefficient, cf. Olson, 1958). After a steady state has been reached, 

 the infra-red illumination is turned off and the dark reaction causes reduction 

 of 'cytochrome 423' at the rate of 0-01 //moles of Fe l.~^ sec~^. The same 

 sample of bacteria is then frozen in an ice-ethanol mixture at a temperature 

 of — 22°C; after solidification has occurred, infra-red illumination again 

 causes the abrupt oxidation of 'cytochrome 423', this time at a rate of 

 0- 1 1 //moles of Fe 1 r^ sec~^, a rate that is practically the same as that meas- 

 ured at room temperature. The final steady state is reached somewhat more 

 slowly than in the room temperature experiment and in accordance with the 

 recognized diphasicity of these reaction kinetics. On cessation of illumination, 



