AGGREGATED CHLOROPHYLL IN VIVO 

 S. S. Brody and M. Brody 



In the introduction (Sections I and II) of this paper, we will cite some of the 

 experimental findings which have been (or can be) interpreted as evidence for 

 the existence of aggregated forms of chlorophyll in solution and in vivo . 

 Although the in vitro systems which we examine involve primarily chlorophyll- 

 chlorophyll interactions, while those in vivo most likely involve, additionally, 

 chlorophyll-protein interaction, we contend that the homogeneous system is 

 the principal one giving rise to the spectral properties seen in nature. 

 Furthermore, we have attributed the numerous peaks in the red end of the 

 absorption spectrum to a) the transitional distributions of chlorophyll 

 aggregates during the formation of the pigment system, and b) to the dis- 

 tributions of chlorophyll aggregates characteristic of the various species of 

 photosynthetic organisms in the"steady state". 



In the body of this paper, (Sections III and IV) we will present some of the 

 recent findings in our laboratories. Certain aspects of these lend further 

 support to our contentions about the existence and role of chlorophyll aggre- 

 gates in photosynthetic organisms. 



I. EVIDENCE FOR THE EXISTENCE OF AGGREGATED FORMS 

 OF CHLOROPHYLL IN SOLUTIONS AND IN LIVING SYSTEMS 



A. The Aggregate in Solution 



1. Evidence Based on Emission : Watson and Livingston (56 ), Lavorel(43), 

 and Weber and Teale (59) have shown that the fluorescence yield of chloro- 

 phyll in solution decreases with increasing concentration above 10"3m. By 

 assuming the formation of non-fluorescent dimers at high concentrations, 

 and calculating the amount of energy transferred to them, Weber (57) effect- 

 ively accounted for the observed decrease in yield. The existence of the 

 aggregated species predicted by these workers was experimentally demon- 

 strated by Brody ( 4 ). He observed emission from an aggregated form of 

 chlorophyll in solution, at 77°K, and reported the maximum of this band to be 

 at 720 mfjL. Its concentration and temperature dependence was described by 

 Brody and Brody ( 9 ). Its low temperature emission was confirmed by 

 Butler (16) and by Stensby and Rosenberg (52). 



455 



