440 HERRICK BALTSCHEFFSKY 



in more detail in other experiments [24]. As another example of the 

 similarities between respiratory electron transport in animal mitochondria 

 and light-induced electron transport in bacterial chromatophores may be 

 mentioned, that also in mitochondria the stimulation of electron transport 

 obtained with menadione is sensitive to antimycin A, as was shown by 

 Conover and Ernster [25], whereas that obtained with PMS is insensitive, 

 as was shown by Kimura and Singer [26]. 



Earlier it has been strongly emphasized that electron transport in 

 oxidative phosphorylation of animal mitochondria and in light-induced 

 phosphorylation of plant chloroplasts and, especially, bacterial chromato- 

 phores shows several similarities [6]. On the basis of data given here this 

 view is further strengthened. For two reasons we consider the chromato- 

 phores of R. ruhrum as being most suitable for studies of the kind presented. 

 The first is that high rates of light-induced phosphorylation are obtained 

 without the addition of any electron carrier. This means that one does not, 

 at least that way, introduce any artificial "by-pass" around a smaller or 

 greater part of the physiological electron transport system. The second 

 reason is that one may select one of two separate cyclic pathways for the 

 electrons to follow, a fact which has opened up new^ possibilities to gain 

 more knowledge about the reactions involved in bacterial light-induced 

 phosphorylation. 



It has been generally assumed, that more than one molecule of ATP may 

 be formed when two electrons are transported through the electron 

 transport chain in light-induced phosphorylation, as has long been known 

 to be the case in oxidative phosphorylation. The three diflFerent kinds of 

 evidence given above provide, when taken together, appreciable support 

 for our opinion that two different sites of ATP-formation exist in " physio- 

 logical " light-induced phosphorylation of chromatophores from R. ruhrum, 

 i.e. for a F/ze^ ratio of 2. 



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