190 1. MALONATE 



coleoptile (Cooil, 1952). These results are plotted in Fig. 1-14-19. On the 

 other hand, rather insignificant effects of pH have been noted in fungi, 

 such as Microsporum, Trichophyton, Epidermophyton (Chattaway et al., 

 1956), and Pullularia (Clark and Wallace, 1958). In Pullularia malonate 

 is readily oxidized; the oxygen uptake from malonate increases with a 

 lowering of the pH along with the inhibition of the cycle and the effects 

 tend to cancel one another. The effects of malonate in tobacco leaves are 

 not changed greatly by lowering the pH from 7 to 4 (Vickery and Palmer, 

 1957), although down to pH 5 the uptake of malonate becomes progressively 

 greater. The incubation here was very long (48 hr) and hence there was 

 more opportunity for malonate to penetrate than in shorter experiments. 

 It is unfortunate that no quantitative work on pH has been done with 

 animal tissues. 



It is also regrettable that in those instances in which malonate inhibits 

 more strongly at low pH values the reversibility of the inhibition has not 

 been adequately tested. Lowering the pH of the medium in the presence 

 of a weak acid increases the amount of unionized acid entering the cells 

 and can decrease the intracellular pH to a degree causing cell damage. It 

 was noted in carrot root tissue that injury to the cells occurred, including 

 loss of turgor and release of some of the cell contents, with malonate at a 

 pH around 4 (Hanly et al., 1952). It is very difficult in experiments of this 

 type to distinguish between a specific malonate effect and a nonspecific 

 acid damage. Examination of the reversibility of the inhibitions might 

 provide some evidence on this point. 



In Volume I it was shown that the intracellular concentration of a di- 

 carboxylate anion is related to the total external concentration in the follow- 

 ing manner (Eq. I-i4-178): 



(i=), = I J; (!,)„ (1-4) 



oJi \n. )'i 



where the subscripts o and i refer to outside and inside the cells and ^f-' 

 is the appropriate pH function for the external inhibitor (see Eq. 1-14-12). 

 Two assumptions are involved in this formulation: (1) only the Hgl form 

 of the inhibitor penetrates, and (2) the cells are internally completely buf- 

 fered. The variation of the intracellular active 1= form with external pH 

 is very marked, as shown in the accompanying tabulation, assuming an 

 intracellular pH, of 6.8. Of course, cells are not completely buffered and, 

 as the internal pH, drops, the entrance of the inhibitor is slowed, so that 

 with decrease in the buffering capacity the ratios given will be lessened. 

 Here one is presented with the dilemma that at low pH values one must 

 either assume a high internal inhibitor concentration or a significant fall 

 in pH,. Since the inhibitions observed are not as high as would be predicted 

 on the basis of the above equation and tabulation, one is forced to conclude 



