SPECTRAL PROPERTIES OF CELLULAR PIGMENTS 



17 



ments, such as cytochromes and anthocyanins, the spectra of which 

 are much the same in pure solution and in the Hving cells. 



In living cells the absorption peaks are lower and broader. The 

 lowering of the peak absorption and the broadening of the curves is 

 known as the flattening effect, some aspects of which have been 

 described mathematically by Duysens (1956). In brief, a part of this 

 effect is caused by the occurrence of the pigments in living cells as 

 small solid particles. In the spaces between these particles the light 

 can come through without being absorbed; hence the lower value of 

 the absorption maxima. These particles are highly enough colored 

 that the absorption may be practically complete within a single 

 particle. Therefore another particle behind it cannot greatly influence 

 the spectrum at the height of the peak, but only in regions of greater 

 transparency. 



The spectra of pigments in intact living cells, with all their compli- 

 cated structures, might well be different from those in alcohol extracts 



400 



450 



600 



iSO 



700 



750 



Wovelength.ffl^ 



Fig. 2. The absorption spectra of the same amount of chlorophyll a in 

 alcohol and in water 1 and 25 min. after dilution. Opal glass was used 

 with all three samples to reduce scattering effects from the colloidal 

 water solution and to make the slit widths identical. 



for several reasons. Comparable flattening, however, may be seen in 

 a much simpler system, as shown in Fig. 2, Here the absorption of a 

 dilute solution of chlorophyll a in alcohol is shown by the upper 

 curve. The same amount of chlorophyll in a small volume of alcohol 



