MECHANISMS OF LIGHT-ACTIVATED ELECTRON 



TRANSPORT IN BACTERIA: THE EFFECT OF 



VISCOSITY ON REACTION RATESl 



BRITTON CHANCE, MITSUO NISHIMURA, S. B. ROY, 

 aiid HEINZ SCHLEYER 



Johnson Research Foundation, University of Pennsylvania, 

 Philadelphia 4, Pennsylvania 



Mechanisms of electron transfer and electron transport in light- 

 and oxygen- induced phosphorylation systems have been a matter of 

 considerable discussion and speculation for some years (1-3), In 

 photosynthetic bacteria, conditions are highly favorable for a detailed 

 examination of the reaction mechanisms (4) which occur; and in this 

 paper we wish to compare the effect of two parameters, temperature 

 and viscosity, upon the light- induced reaction velocity (5,6). Where 

 possible, similarities and differences of reaction mechanisms in light- 

 induced systems will be compared with those observed in systems 

 involving oxygen- induced electron transfer. 



Configuration of electron transport chain. 



It is appropriate to compare the nature of the electron transport 

 chain of the chromatophore with that of the elementary unit of oxygen- 

 linked electron transfer which has recently been christened "oxysome" 

 (7). (See Fig. 1,) 



The configuration employed here emphasizes the similarities be- 

 tween the two systems, at least insofar as the electron-accepting 

 properties of oxygen and chlorophyll are concerned. A chief differ- 

 ence, of course, is found in the electron-donating properties of chloro- 

 phyll which, at least in the green plants, appear to lead to pyridine 

 nucleotide reduction by an electron transport pathway involving the 

 pyridine nucleotide reductase system. As a matter of fact, this dif- 

 ference is relatively superficial when we include in the oxygen-linked 

 system the well-established observation that internal high energy in- 

 termediates generated in oxidative phosphorylation lead to a side path- 

 way of pyridine nucleotide reductionas well. In fact, it is even possible 

 that a similar pathway is highly active in the photosynthetic system, 

 according to the results of Gest and Bose (8), In general, we see only 

 one essential point of difference between the light- and oxygen- 

 1 This research is supported in part by the National Science Foundation, Pub- 

 lic Health Service, and Office of Naval Research. 



357 



