EFFECTS ON THE ENDOGENOUS RESPIRATION 185 



Substrate metabolism R.Q. 



Glucose -> CO2 + H2O 1.0 



Glucose -> succinate -f CO2 + H^O 0.8 



Glucose + 2 oxalacetate ->• CO2 + HgO 1.27 



Glucose + 2 oxalacetate -> 2 succinate + CO2 + H2O 1.5 



Pyruvate -> COj + HjO 1.2 



2 PjTuvate -> succinate + CO2 + H2O 1 . 33 



Pyruvate + oxalacetate -> COj + H2O 1.4 



Pyruvate + oxalacetate ->■ succinate + COj + O2 2.0 



ButjTate -^ CO2 + H2O 0.8 



ButjTate -r oxalacetate -> COj + HjO 1 . 23 



Butyrate + oxalacetate -> succinate + CO2 + HjO 1.0 



Butyrate + 2 oxalacetate -> CO2 + HjO 1.2 



But>Tate + 2 oxalacetate -> 2 succinate + CO2 + H2O 1.33 



1937). However, malonate decreases the R.Q. of kidney slices, both en- 

 dogenous and with pyruvate as the substrate. Malonate elevates the R.Q. 

 of rat adipose tissue from 1.0 to 1.13 endogenously and from 1.14 to 1.41 

 in the presence of glucose (Haugaard and Marsh, 1952). In frog muscle, 

 the R.Q. first rises from 0.9 to 0.97 at 10 mM malonate, but then progres- 

 sively decreases as the malonate concentration is raised so that at 200 mM 

 malonate the R.Q. is 0.39 (Thunberg, 1909). In plant tissues, the effects 

 are less variable. Malonate has been shown to increase the R.Q. of barley 

 roots from 0.97 to 1.14 (Machlis, 1944), of maize roots (Beevers, 1952), 

 of carrot roots up to values as high as 3 (Hanly et al., 1952), of chicory 

 roots from 1.03 to 1.14 (Laties, 1959 a), and of rhubarb leaves at pH 5.3 

 (Morrison, 1950). 



Of course, there are many factors which must be taken into account, 

 since malonate can secondarily alter several metabolic pathways. A stimula- 

 tion of glucose uptake could change the R.Q. in either direction, depending 

 on the nature of the substrates used in the uninhibited tissue; in the pre- 

 sence of a significant cycle block, this would usually depress the R.Q. and 

 counteract the more direct effects described above. On the other hand, 

 metabolism of malonate would tend to elevate the R.Q. since the complete 

 oxidation would give R.Q.'s of 1.50-1.55 and the oxidation to succinate 

 3.0-4.0. A final factor of importance is the relative dependence of glucose 

 and fatty acid metabolism on the operation of the cycle and the levels of 

 ATP, since malonate could alter the oxidative contribution from these sub- 

 strates secondarily. 



