Haem Protein Content and Function in Relation to 



Structure and Early Photochemical Processes in 



Bacterial Chromatophores* 



AIartix D. Kamen 



Brandeis L uiversity, 

 Waltham, Mass., U.S.A. 



The essential process in photosynthesis is the absorption and conversion 

 of radiant energy into chemical free energy with subsequent storage in a 

 form which can be used for biosynthesis. Currently, the most widely 

 studied example of this process in cell-free systems is " photophosphoryla- 

 tion" — the chromatophore, or chloroplast, catalysis of ATP synthesis 

 from ADP and inorganic phosphorus, utilizing energy absorbed by the 

 photoactive pigments contained in these particles. 



The time during which the energy conversion and stabilization phase 

 of photosynthesis occurs is subsumed between ^ lo " sec. and ~ lo ~- sec. 

 The former limit is set by the time required for initial quantum absorption 

 and subsequent migration of the energy packet to the active centre of the 

 system by processes such as exciton migration, or induced resonance, 

 which depend in detail on the specific structural features of the photo- 

 active particles. It is possible that stabilization of the excitation energy in 

 the so-called "triplet" state of the photoactiye pigment can extend the 

 upper boundary in time from lo^^ sec. to lo^ sec. [i]. The latter limit 

 is given by the ayerage turno\"er number of enzymes invoked in the 

 biochemical processes which lead eventually from assimilation of CO., or 

 organic material to synthesis of cell material. 



We know very little about the photochemical processes which occur 

 during this critical interval in time. A basic question which highlights this 

 ignorance is : What molecular composition and placement is both necessary 

 and sufficient to bridge the gap between quantum absorption and 

 biosyntheses ? 



We may suppose that some sub-unit of the plant granum or bacterial 



* Communication Xo. i i i in the series "Publications of the Graduate Depart- 

 ment of Biochemistry, Brandeis University". Researches in this laboratory on 

 which this paper is based have been supported by grants from the National 

 Science Foundation (Grant Xo. Cj-6441) and the Xational Institutes of Health 

 (Grant Xo. C-3649). 



