EFFECTS ON RESPIRATION 



489 



example, which is quite typical, is illustrated in Fig, 5-4. In other cases 

 only respiratory stimulation has been reported, although it is likely that 

 inhibition would have been noted at higher quinone concentrations. We 

 have discussed the augmentation of respiration in brain (Hoskin, 1960 b) 

 and leucocytes (Iyer et al., 1961) by menadione. The effects on erythrocyte 

 respiration apparently involve special mechanisms and are not completely 

 understood. Friedheim (1934) noted that juglone and lawsone at 1 mM in- 

 crease the oxygen uptake of rabbit erythrocytes 5- to 6-fold in the presence 



Fig. 5-4. Effects of 1,4-NQ on the respiration 



and luminescence of bacteria. (From Spruit and 



Schuiling, 1945.) 



of glucose, and claimed that the effect is not linked to the hemoglobin 

 redox system since he could detect no formation of methemoglobin. Lovell 

 and Prankerd (1961) pointed out that the small respiration of erythrocytes 

 is probably related to the oxidation of hemoglobin, and then showed quite 

 conclusively that 1,4-naphthoquinone and menadione cause a rapid oxi- 

 dation of hemoglobin to methemoglobin, and a corresponding augmentation 

 of the oxygen uptake. Harley and Robin (1963) also showed that 1,2- 

 naphthoquinone, 1,4-naphthoquinone, and menadione catalyze the conver- 

 sion of hemoglobin to methemoglobin; e. g., at a molar ratio of 1,2-naphtho- 

 quinone to heme of 1:32, 60% of the hemoglobin is oxidized in 4 hr. The 

 reaction is apparently dependent on NADPH and is thereby related to 

 the operation of the pentose-P pathway, which can normally provide 



