530 



John A. Bergeron 



contain 6.9U x 10 molecules of chlorophyll. The lamellar area 

 available for chlorophyll (each membrane has two sides, the innei> 

 most is treated as a half) is I.83 x 109 A^ or 272 K^ per molecuLa 

 Sinc| the area of the "head" of the chlorophyll molecule is about 

 225 A^ all of the chlorophyll could be accommodated in the cyto- 

 plasmic membranes -v^ich occur in the fluorescent cortical region. 



The cortical volixme was calculated (6.U3 x 10"^ cc) and used 

 to estimate the cortical concentration of phycocyanin {k.2k to 

 8.52 X 10" M). At this concentration the maxim\un possible uni- 

 form separation between adjacent molecules is between 12l4- and I56 

 A. For spherical protein molecules in the molecular weight^range 

 of l.k to 2,8 X 105 gm/mole the diameter would be 70 to 90 A. 

 This maximum possible uniform spacing would leave the molecules 

 less than a molecular diameter apart. It seems likely that the 

 phycocyanin molecules exist between the lamellae in a state in 

 •v^ich molecular interaction is probable. These observations are 

 not consistent with the hypothesis that phycocyanin is related to 

 one pool of chlorophyll and remote from another of equal size. 

 Another explanation should be provided to account for the appar- 

 ently greater efficiency of phycocyanin in producing chlorophyll 

 fluorescence (see below). 



PETySICOCHB^ICAL STATE OF PHYCOCYANIN IN VIVO 



It is knownV 22-24) that phycocyanin dissociates reversibly in 

 the pH range between 6 and 7. Apparently investigators interest- 

 ed in the photosynthetic activity of this protein have not con- 

 sidered the potential significance of this property. 



Phycocyanin was released from Anacystis nidulans by rupturing 

 the organisms in a French pressure cell in phosphate buffer (O.l 

 M, pH 5.7). The purification, excepting the precaution of not 

 allowing the pH to rise above 5.7, followed the procedure of 

 Hattori and Fujita(2^). Figure h illustrates that there is a 

 decrease in absorption of the 621 mn maximum and a broadening of 

 the band width over the pH range where dissociation occurs. The 

 fluorescence of the protein also changes. Figure 5 illustrates 

 that the dimer possesses a fluorescence maximum at 68O mpi which 

 is depressed for the monomer. When molecular interaction is en- 

 hanced by the addition of ammoniiam sulfate, the 660 mn maximum 

 is depressed leaving the 68O mn band as the maximijm. By contrast^ 

 monaneric phycocyanin, similarly treated, does not show a com- 

 parable alteration of the fluorescence spectrum. These observa- 

 tions provide an alternative explanation for the results obtained 

 for the fluorescence of blue-green algae since piirified 



I 



