1612 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



Macdowall (1949) found that 2 X 10 ~' M phenylurethan are required for 

 a 50% inhibition with quinone (table 35.XI). Arnon and Whatley (1949) 

 found a higher sensitivity — nearer that observed by Hill and Warburg, 

 than that observed by Aronoff and Macdowall. 



Wessels (1954) found incomplete inhibition by 3 X 10~' mole/1, 

 phenylurethan of the photoreduction of benzoquinone, but a complete 

 inhibition of that of 2,6-dichlorophenol-indophenol; the latter was 50% 

 inhibited by 3 X 10"" mole/1. Davenport et al. (1952) observed 50% 

 inhibition at 1.2 X 10~^ mole/1, phenylurethan (or 0.35 mole/1, ethyl- 

 urethan) of the methemoglobin reduction in crude chloroplast suspensions. 



Warburg and Liittgens (1946) observed that the quinone reaction is 

 completely inhibited in a saturated solution of octanol. 



Other Inhibitors. Macdowall (1949) made a study of the inhibition 



Table 35.XI 



Inhibition of Hill Reaction in Chloroplasts from Spinach or Swiss Chard with 

 Phenol-Indophenol as Oxidant (after Macdowall, 1949) 



Concentration 

 producing 



50% 

 inhibition, Inhibition occurs 



Inhibitor mole/liter in strong or weak light 



Poisons of Heavy Metal Prosthetic Groups 



Cyanide" >0 . 01 — 



Azide" . 08 In strong light 



Pyrophosphate >0. 1 — 



Hydroxylamine" 3 X 10"" Equally in both 



Resorcinol . 09 Equally in both 



o-Phenanthroline" 2 . 7 X 10~^ In both, but more pronounced 



in weak light 

 Thiourea 0. 15 — 



Poisons of Sulfhydryl Groups* 



Dinitrophenol" 6 X 10~^ In both, but more pronounced 



in weak light 

 lodoacetate'' 0.01 In strong light 



Heavy Metal Ions 



Cu"^^ '' IX 10~^ Much stronger in weak light 



Hg+2 '> 4 X 10"^ More pronounced in strong 



light 



Narcotics 



Phenylurethan 2 X 10~' Stronger in weak light 



Thymol* 2 X lO"' Equally in both 



Chloroform . 03 Stronger in weak light 



Ether 0.5 



Strychnine >1.0 Stimulation in strong, inhibi- 



tion in weak light 



" Cf. other data above. 

 * Cf. Wessels' data below. 



