528 



John A. Bergeron 



LOCALIZATION AND INTRACELLULAR CONCENTRATION 

 OF THE PHOTOSYNTHETIC PIGMENTS 



It is important to know not only the intracellular localiza- 

 tion of phycocyanin, but also the relationship of phycocyanin to 

 the chlorophyll -bearing structures. Electron. microscopic obser- 

 vations on a number of blue-green algae^ '' have established 

 the presence of triple -layered cytoplasmic lamellae as a consis- 

 tent feature. It is known that the chlorophyll containing parti- 

 cles, free of phycocyanin, obtained by fractionation of broken 

 cells consist of lamellar fragment sv 13 ) . While it is clear that 

 the cytoplasmic membranes Contain chlorophyll and that the integ- 

 rity of these membranes does not depend upon a fixed relationship 

 with phycocyanin; the relationship of these membranes to phycocy- 

 anin and the physical basis for the concept of two pools of 

 chlorophyll has remained obscure. 



Our approach to these questions has been based upon the follow- 

 ing types of observations; spectrophotometric studies of the pig- 

 ments coupled with cell counts and cell volume determinations, 

 dark field fluorescence microscopy of normal organisms and organ- 

 isms repeatedly extracted in 80^ acetone, and electron microscopy 

 of intact organisms and subcellular preparations. 



The concentration of chlorophyll a and phycocyanin in cell 

 suspensions was calculated by the procedure of Kratz and Meyersi^' 

 from the absorption spectra. Opal glass was used to reduce the 

 effect of light scattering. The concentration of organisms in 

 the suspensions was calculated from measurements with a Petroff- 

 Hausser bacteria counter. These n\jmbers suffice to calculate the 

 pigment content of the cells. For typical type E cellsv^^) from 

 log phase the average chlorophyll content was 2.05 x 10~11 mg6ell 

 or 1.3 X 10' molecules. The phycocyanin content was 1.52 x lO'^*-^ 

 mg/cell or 3 '27 to 6.5U x 105 molecules depending upon the as- 

 signed molecular weight (see below). An average cell volume was 

 calculated fran measurements (n = 50) of the length and diameter 

 of these cells from phase contrast micrographs taken at known 

 magnification and enlarged upon Resist© paper. From the mean 

 diameter (O.92 ± 0.01 n) and length (2.67 ± 0.82 |i) the mean vol- 

 ume was calculated as the sum of two hemispheres and a right cyl- 

 inder (H = L - D) . The average volume was I.58 x 10~12 cc. On 

 this volume basis the intracellular pigment concentration, ex- 

 pressed over the entire cell, is l.kk x 10"2 M for chlorophyll 

 and 3.1|4 to 6.88 x 10"^ M for phycocyanin. 



It is easy to observe, but difficult to record by photography. 



