520 



Eiji Fujimori and Kenneth Quinlan 



PHYCOERYTHRIN 



Treatment of purified phycoerythrin from Ceramium rubrum with PCMB 

 eliminates the 565 m;j. absorption band from the visible spectrum ^ ' . This 

 same effect has been found in the present study with purified phycoery- 

 thrin from Porphyridium cruentum. Fig. 1 shows the disappearance of the 

 565 m/ut band with the 500 rr^uand 545 rrvu. absorption bands remaining in- 

 tact. The latter two absorption bands disappear on reduction with sodium 

 hydrosulfite. Evidence obtained from the present study shows that a seg- 

 ment of the phycoerythrin containing the 500 vrp^ chromophore can be 

 separated from a segment containing the 545 dt/u. and 565 rr^a chromophores. 

 This result will be described below. These studies illustrate the existence 

 of three types of chromophore in phycoerythrin and the influence of sul- 

 fhydryl groups on the 565 rr^ chromophore. 



The addition of PCMB to native phycoerythrin decreases the fluores- 

 cence intensity with time. This result indicated that the 565 m;> chromo- 

 phore is responsible for the radiative transition since the absorption 

 maximum at 565 rryu^ is the only one effected by PCMB. The action spec- 

 trum of the fluorescence (Fig. 2) shows also the participation of the 500 irys 

 and 545 rrjiu. chromophores in transferring energy to the 565 m^u- chromophore. 

 A series of action spectra of the fluorescence of phycoerythrin in the 

 presence of PCMB presented in Fig. 2 shows the decrease of energy trans- 

 fer among the chromophores. Since the 500 rryu and 545 rryj. chromophores 

 can still be excited in the presence of PCMB (Fig. 1), the absorbed 

 energies must now be dissipated in a non-radiative transition. 



The sulfhydryl content of phycoerythrin has been determined by 

 amperometric titrations (Fig, 3), A value of eight sulfhydryl groups per 

 molecule of phycoerythrin has been obtained, assuming a molecular 

 weight of 290,000 ^^' and a specific extinction coefficient of 2.73 at 

 565 rryx ^ ' for phycoerythrin. It is not known what fraction of these 

 sulfhydryl groups are associated with the chromophore. 



PHYCOCYANIN 



The purified phycocyanin from the blue-green alga, Anacystis 

 nidulans, exhibits an apparent single absorption peak at 615 m|j. and a 

 fluorescence at 640 m\y. However, the action spectrum of the 



