DIFFERENT OXIDANTS 



1563 



A chloroplast-free Hill solution itself evolved some gas when illuminated 

 with white light (250 f .-c.) ; to avoid errors due to this evolution, a nitrogen 

 atmosphere and the presence of a 10% KOH solution in a side arm of the 

 manometric vessel were used by Holt and French (1946). With these pre- 

 cautions, all pressure changes observed could be ascribed to oxygen. The 

 addition of inactivated (boiled) chloroplasts to Hill's mixture had no effect. 



100 



° / 



TIME, minutes 



Fig. 35.16. Oxygen production by spinach chloroplasts immersed in various 

 combinations of the constituents of Hill's mixture (after Holt and French 1946): 

 (1) complete mixture; (3) 0.50 M K2C2O4 + 0.02 M K3Fe(CN)6; (5) 0.01 M Fe- 

 (NH4)(S04)2 + 0.02 M K3Fe(CN)6; (4) 0.02 1/ K3Fe(CN)6. 15° C, pH 6.8, all 

 in 0.17 A'' sodium sorbitol borate buffer, 0.28 mg. of chlorophyll per vessel. 



(6) Other Inorganic Oxidants 



Holt and French (1948) investigated a variety of oxidizing agents 

 They used spinach chloroplast fragments in a phosphate buffer in nitrogen 

 atmosphere. Manometric evidence of gas production (and chemical proof 

 that this gas was oxygen) was obtained with chromate [which was earlier 

 found inactive with live Chlorella cells by Fan et al. (1943)] and with m- 

 vanadate (too little O2 for manometric study). Numerous other oxidants 

 gave no oxygen at all, among them molybdate, bromate, chlorate, tetra- 

 thionate, tungstate, hypochlorite, permanganate, nitrate, periodate, bis- 

 muthate, iodine, arsenate, persulfate and perborate. An initial outburst of 

 gas was obtained upon mixing chloroplasts \vith perborate or permanga- 

 nate, but illumination led to no additional gas Hberation. 



