96 MARTIN G. LARRABEE AND PAUL HOROWICZ 



Proceeding on the assumption that all the glucose not converted to lactate 

 was completely oxidized, some calculations can be made. Per gram of dry tis- 

 sue per hour the average rates during the first two hours were 11.7 mg. of 

 glucose consumed and 3.5 mg. of lactate produced. The difference, 8.2 mg. of 

 glucose, was thus left over for oxidation. Assuming that this residue was all 

 completely oxidized, stoichiometric relations permit the calculation that 273 

 micromoles of oxygen would have been required per dry gm. hour. Actually 

 the observed oxygen uptake was 298 micromoles per dry gm. hour, as stated 

 above. 



Thus it is highly probable that exogenous glucose is the main substrate for 

 resting oxidations in a ganglion, in agreement with conclusions for other nerv- 

 ous tissues. It is possible that under the conditions of our experiments there 

 was, in addition, some oxidation of endogenous substrates, since the observed 

 oxygen uptake exceeded the calculated rate by 25 micromoles per dry gm. hr. 

 However, this difference is not statistically significant, since it is less than 2 

 times the standard error, as calculated from the standard errors of the glu- 

 cose, lactate, and oxygen data. Moreover, there were some systematic dif- 

 ferences between the conditions for the various measurements. We have thus 

 been unable either to prove or disprove a slow oxidation of endogenous sub- 

 strates under the conditions of our experiments. The important conclusion is 

 that glucose is the major substrate for oxidation in a ganglion at rest. 



Our results are in agreement with the conclusion reached by others that 

 only a small fraction of the useful energy generated intracellularly is derived 

 non-oxidatively from glycolysis. This is perhaps indicated most clearly by 

 attempting to calculate the yield of so-called high energy phosphate bonds 

 (~P) from our metabolic measurements. Provisionally we have assumed that 

 the consumption of each atom of oxygen was accompanied by the formation of 

 three molecules of ~P, in agreement with average P/O ratios observed under 

 optimal conditions in various tissue preparations (Lehninger, 1953-54). The 

 validity of this assumption will be considered below. We may also assume that 

 in addition to the oxidative generation of ~P, two molecules of this material 

 were formed for each molecule of glucose consumed, in accordance with the 

 Embden-Meyerhof schema of glycolysis. Results of the calculations suggest 

 that about 95% of the so-called high energy phosphate bonds were generated 

 by oxidations (Table IV). This percentage must be regarded as only a rough 

 approximation to the true value since it is by no means certain that the P/O 

 ratio is as high as 3 in intact cells (Lehninger, 1953-54). However, it is not un- 

 reasonable to assume that the normal P/O ratio is at least high enough so that 

 most of the useful energy obtained from glucose metabolism through media- 

 tion of phosphate bonds does indeed come from oxidations. 



With the realization that the results can only be construed as approximations, 

 we have also calculated the ~P yields in the absence of glucose and in the ab- 



