RESPIRATION 



885 



has not been investigated sufficiently to draw valid conclusions. Of course, 

 in tissues such as most muscle and heart, in which endogenous substrates 

 are responsible for the bulk or all of the respiration for some after time ex- 

 cision, glucose would not be expected to have much effect on the inhibition 

 by mercurials. Little is known about the effects of mercurials on the pen- 

 tose-? pathway or other routes of glucose degradation. In crude extracts 

 of Pseudomonas converting gluconate-6-P to 3-phosphoglyceraldehyde and 



12- 



09 



1000 



- 800 



0.6-1 



^ 0.3 - 



- 600 



-400 



i-o 



Fig. 7-34. Effects of Hg++ on the respiration and the 



levels of substances in yeast. Concentrations given as 



/*moles/g dry weight. Run at pH 6.8 for 60 min. (From 



Estler et al., 1960.) 



pyruvate, p-MB at 1 mM inhibits completely (Kovachevich and Wood, 

 1955). The site of the inhibition is not clear, but it is presumably not on 

 the gluconate-6-P dehydrase, which was purified and found to be only 

 moderately sensitive to p-MB. The pentose-P pathway is operative in ex- 

 tracts of tobacco leaves, the oxidations being NADP specific, and p-MB 

 at 0.1 mM almost completely blocks the reduction of NADP by both glu- 

 cose-6-P and fructose- 1,6-diP (Clayton, 1959). The utilization of pentose-P 

 by extracts of Lactobacillus hrevis is inhibited only 20% by 0.1 milf p-MB 



