with - and, I think, only obtainable with - syn- 

 chronized single generation cultures, which sup- 

 port this general picture that I have been trying 

 to create. 



One of the first changes induced by bicar- 

 bonate, and detectable in vivo immediately after 

 spore germination, has to do with gas exchange 

 (Fig. 4). The upper curve reveals the course of 

 oxygen consumption by an OC cell growing in 

 the absence of bicarbonate. The lower curve 

 shows what happens when bicarbonate is present 

 in the medium. After the spore has germinated, 

 there occurs an immediate and precipitous drop 

 in oxygen consumption. Simultaneously, the ex- 

 ponential growth rate is reduced to 46% of that 

 of the cell growing in the absence of bicarbonate. 

 Also, bicarbonate causes the exponential rate of 

 synthesis of the cell's pool of a soluble poly- 

 saccharide (made up solely of glucose) to double 

 relative to the cell's exponential rate of growth 

 in mass. These facts do not, of course, prove 

 that lesions have developed in the tricarboxylic 

 acid cycle as outlined above; they are, however, 

 consistent with this interpretation. 



The available quantitative data which deal 

 with the enzymes themselves have a direct 

 bearing at this point in our discussion. For ex- 

 ample, cells growing along both developmental 

 pathways have been assayed at various stages 

 in ontogeny for isocitric dehydrogenase and 

 ketoglutaric dehydrogenase activities. When the 

 data are plotted, not as specific activities but 

 rather as total units of enzyme activity per 

 cell, it turns out that the exponential rate at 

 which isocitric dehydrogenase accumulates in 

 the cell during its exponential growth phase is 

 about seven times higher than the rate at which 

 the ketoglutaric dehydrogenase complex does 



SIMULTANEOUSLY 1 



EXPONENTIAL GROWTH RATE 

 IS REDUCED BY 45% 

 AND 

 EXPONENTIAL SYNTHESIS OF 

 POLYSACCHARIDE / DRY 

 WEIGHT INCREASED 100% 



SO (Fig. 5). Furthermore, as will be seen 

 shortly, the net accumulation of this latter 

 enzyme system in the cell levels off and ceases 

 long before that of isocitric dehydrogenase. 

 What does this observation have to do with the 

 question of oxygen consumption? A glance back 

 at the previous slide will show that during the 

 exponential growth of a developing RS cell, oxy- 

 gen consumption decreases to about one-tenth 

 of its startinglevel(Qo2 = ^^- 100) in the spore. 

 If oxygen consumption by the growing cell were 

 totally and exclusively dependent upon the opera- 

 tion of the tricarboxylic acid cycle, one might 

 expect that the rate of turnover of the cycle 

 would also drop to one-tenth of its starting rate 

 at zero time. The quantitative data associated 

 with Fig. 5 are consistent with this thought. From 

 spore stage to end of exponential growth, the 

 total units of isocitric dehydrogenase per cell 

 increase 6,500 times, but the total units of 



10- 



UJ 



o 



(/) 3. 



z 

 



'a KETOGLUTARIC 

 DEHYDROGENASE 



40 60 



% GENERATION TIME 



100 



HOURS 



Fig. 5. 



24 



Fig. 4. 

 Oxygen consumption by OC and RS cells. 



A comparison of the exponential rates of synthesis of 

 Isocitric and a -ketoglutaric dehydrogenase per RS cell 

 during exponential growth. 



152 



