716 



William F. Prickett, F. Dudley Bryant, and Paul Latinner 



ADDENDUM 

 (added during the meeting) 



At this meeting Dr. R. A. Olsen gave further evidence of the presence 

 in chloroplasts of a pigment with an absorption maximum near 700 m/i. His 

 studies of absorption and fluorescence indicate that molecules of this pigment 

 are highly oriented with respective dipoles being parallel to one another. We 

 here give other evidence of this pigment based on a new interpretation of pre- 

 viously reported double refraction spectra of Mougeotia cells. 



Goedheer and also Menke and Menke (see Ref. 21 and 2Z of the above Ref. 

 6) reported spectral birefringence curves which display strong anomalous dis- 

 persion effects caused by the chlorophylls. Such effects can be produced by two 

 mechanisms: one, by the pigment molecules residing only in every other layer 

 of the granum (form birefringence), and two, by the pigment molecules being 

 spacially oriented (orientation birefringence). On a per molecule basis, the 

 orientation mechanism is much more efficient. It has been frequently assumed 

 that these authors' curves were produced by form birefringence only. However, 

 especially in the case of mature cells, the spectral birefringence curves are 

 symmetrical about a wavelength near 690 m^ instead of near 675 m^, the nom- 

 inal position of the main chlorophyll maxinnum. There are no conditions under 

 which dispersion theory can predict a shift of the center of an anomalous dis- 

 persion curve away from the absorption maximum of the pigments producing it. 

 Hence the birefringence curves must have been strongly influenced by pigment 

 molecules absorbing near 700 mji. 



The most likely explanation is that the observed birefringence is caused 

 by a combination of the above sources. The form birefringence is produced by 

 the predominant 675 mfx band (or components thereof). Molecules of this band 

 are not spacially oriented as indicated by Olsen. The orientation birefringence 

 is produced by the less prevalent but highly oriented molecules with an absorp- 

 tion maximum near 700 m/i. Our approximate calculations, based on the above 

 data, suggest that the concentration of this latter pigment can be as high as 10% 

 of the total pigments producing the 675 mfi band (this assumes a 700 m/i mole- 

 cule with the extinction coefficient of chlorophyll a). Perhaps this 700 m/i pig- 

 ment is that of case III above, the presence of which in spinach chloroplasts 

 was indicated by our approximate absorption spectrum analysis. 



