98 



¥. L. Butler and N. I. Bishop 



The other set of mutants, called "O2" mutants, fails to evolve 

 O2 in the light but will photoreduce CO2 in a hydrogen atmos- 

 phere. These mutants show a high fluorescence yield (Fig. 3) 

 which is not affected by actinic light. These measurements are 

 consistent with the photochemical activities of the "O2" mutants 

 which indicate that system 1 is operating, since CO2 can be 

 photoreduced with H2j tiut that system 2 or some reaction closely 

 allied with O2 evolution is not functioning. 



Low-temperature absorption and derivative spectra of the wild- 

 type and mutant cells are shown in Fig. U. The derivative 

 spectra were used primarily to distinguish the presence of P, the 

 small amount of chlorophyll absorbing near 700 nm. The 



1 — . — . — , — 1 — r 

 absorption 



derivative 



wild type 



1— Oo mutant 



COj mutant 



400 



500 



600 700 

 WAVELENGTH -nm 



600 



700 



Fig. U. Absorption and derivative spectra of Scenedesmus 

 wild-type, "O2" mutant No. 11 and "CO2" mutant 

 No. 8 cells at -196°C. 



