BACTERIAL PHOTOSYNTHESIS 



183 



trifugation for 90 minutes at 144,000 g in the same medium. For 

 some purposes the chromatophores can be washed by repeated 

 centrifugation in dikite buffer or distilled water. The isolated 

 chromatophores can be lyophilized and stored over phosphorus 

 pentoxide at reduced temperature (—20° C) for long periods with- 

 out significant loss in enzymic activity or alteration in the over-all 

 phvsicochemical properties. 



Physicochemical Properties. About 90 per cent of the cellular 

 pigments are recovered in the final fraction. The absorption spec- 

 trum between 350 m^u and 1000 m/>i of the chromatophores prepared 

 in the sucrose medium corresponds with the absorption spectrum of 

 the original cells (Fig. 3). It might be expected, a priori, that the 

 chromatophores are rather fragile, but the reverse is true. Prolonged 

 oscillation at 10 kilocycles in dilute buffer does not produce appre- 

 ciable fragmentation. The chromatophore is hydrophilic and has 

 an isoelectric point between pH 3 and 4; this is in accordance with 



0.8- 



0.2 



WHOLE CELLS AND CHROMATOPHORES 

 IN SUCROSE 



400 500 600 700 800 



X (MILLIMICRONS) 



900 



Fig. 3. A spectrophotometric comparison of chromatophores, isolated in the 

 buffered 0.5M sucrose medium, with the intact organisms, suspended in Hendley's 

 medium. The spectra were measured (Cary Model 14) through opal glass to 

 reduce the divergence caused by light-scattering at the lower wave lengths. 

 The close correspondence indicates that the photosynthetic pigments are not 

 disturbed by this isolation procedure. 



