86 



Walter Bonner and Robert Hill 



The spectrum of Figure 4 shows the ei -band of cytochrome JE and 

 some semblence of the 3-band; the complete absence of the 518 

 response is worthy of note. In this spectrum 559 m^i appears to 

 be isosbestic and at longer wave-lengths there is a region of 

 decreased transmission, a decrease in transmission that could be 

 interpreted as light induced cytochrome b^ reduction. In these 

 experiments there were suggestions that as the mung bean leaves 

 formed chlorophyll the ©(-band of cytochrome b^ became broader 

 and shifted toward the red. However, if one measured, during 

 greening, both the amount of chlorophyll and the amount of cyto- 

 chrome b^ using visual optical methods (a direct-vision micro- 

 spectroscope, the optical path of the comparison prism being 

 equipped with two wedged troughs containing respectively a 

 standard chlorophyll a solution and a standard hemochromogen 

 solution) it was observed that cytochrome b^ gradually disap- 

 peared as the chlorophyll concentration increased but theo^-band 

 of cytochrome b^ remained remarkedly sharp at 560 mp, as long as 

 it could be observed. The results from experiments using both 

 the differential spectrophotometer and the direct vision micro- 

 spectroscope can be interpreted in three ways: 1) There is 

 formation of a chlorophyll-cytochrome complex, a complex which 

 could be similar to that of Takamiya et. al^, (this symposium). 

 In the case of the mung bean leaf the complex would be between 

 cytochrome b^ and chlorophyll a since only chlorophyll a is 

 formed during these early stages of greening; 2) One is observ- 

 ing the light activated oxidation of cytochrome bg an oxidation 

 that requires a higher chlorophyll concentration than the corres- 

 ponding reaction with cytochrome f_; 3) The fact that in the 

 partially greened leaf (and in the fully greened leaf also) there 

 is no light induced optical response in the region of cytochrome 

 b5 oC-band absorption (560-570 mn) while mder the same condi- 

 tions there is a rapid light induced oxidation of cytochrome f 

 might point to the conclusion that cytochrome b^ does not par~ 

 ticipate in light activated electron transport. 



Oxidized cytochrome f^, like oxidized cytochrome c, possesses 

 a region of steadily increasing opacity in the region 560-570 mn; 

 the transmission decrease between 560 and 570 mn shown in the 

 spectrum of Figure 4 can be interpreted as being caused by the 

 formation of oxidized cytochrome f^. For this reason and because 

 the spectrum of cytochrome b^ remains sharp up to the point of 

 its disappearance, the gradual disappearance of cytochrome bg 

 with greening appears to be caused by a light activated oxidation 

 of this component. In these experiments a light induced cyto- 

 chrome b^ reduction was observed, but only in ruptured chloro- 



