476 



S. S. Brody and M. Brody 



We are in the process of identifying the petroleum either 'residue', and of 

 determining if there is more than one naturally occuring quencher in chloro- 

 plasts. So far, we have found that the 'residue' of the petroleum ether 

 washings has some of the properties of a terpenoid quinone (such as plasto- 

 quinone or coenzyne Q). 



Since the naturally occuring quencher ('residue') is not readily removed 

 from chlorophyll a, even after repeated chromatography, it nnay be that it 

 is strongly complexed with chlorophyll. This contention is supported by the 

 fact that even in very minute amounts it will quench emission at 698 my.. The 

 ease with which this excited state is quenched is significant for it suggests 

 that the excited state may be effective in sensitizing photoreactions. 



F. Excitation Spectra in Solution and In Vivo 



In Fig. 20 may be seen an excitation spectrum (for emission at 730 mji) 

 determined with Euglena (in light 80 hours) at 77°K; it contains a band with 

 maximum at 708 m|ji. The general features of this spectrum are similar to 

 the excitation spectrum (for emission at 736 mjj,) determined with a concen- 

 trated solution of chlorophyll in pyridine (10 "^M) at 77°K; in Fig. 20 may be 

 seen a band with maximum at 718 mfjL which we feel corresponds to the 708 my 

 band in vivo . Similar experiments with dilute solutions cf chlorophyll yield 

 excitation spectra (for emission at 726 mij.) which do not contain the band at 

 718 my., (or for that matter, any bands at all between the monomer absorp- 

 tion maximum at 680 m|j. and the emission maximum at 736 m|j.); see Fig. 20. 



Fig. 20 Excitation spectra for dilute and concentrated solutions of chloro- 

 phyll a in pyridine, and Euglena, at 77°K; wavelengths being monitored given 

 in text. 



With very young Euglena (in light only a few hours) the band at 708 my is 

 only a small shoulder. All of our data on the 708 band in vivo has not yet 

 been analyzed in a quantitative fashion, however, it appears at least qual- 

 itatively - that the magnitude of this absorption band and the intensity of the 

 emission band between 720 and 730 my increase in a parallel fashion. In 

 light of the above findings, we would like to suggest that it nnay not be nec- 

 essary to assume a colorophyll-cytochrome complex (16) to account for 



