260 



GERTRUDE E. CLOCK 



TABLE II 

 Ci Recovery in CO2 Produced During Glucose Utilization by 



E. COLT 



Recovery^ 

 Moles BaCOa ," Recovery'' Ci 



Physiological COj/mol. cts./min./ Ci in CO2 , (theory), Excess 



condition glucose mg. C per cent per cent per cent 



Oxidation without 



growth 3.22 212 54.4 53.7 0.7 



Growth 1.32 156 37.7 22.0 15.7 



T2 synthesis 1.38 121 29.1 23.0 6.1 



" After known dilution of CO2 with carbonate. 

 ''Calculated from the following equation: 



„ BaCOa isolated X specific activity (BaC03)/mg. C X 100 



TV) recovery ^^ ^ 



/iM. glucose X mol. wt. BaCOa X specific activity (glucose-Ci) 



*■ Calculated from maximal liberation of isotope from CHj-labeled pyruvate 



or n :„ no moles C02 liberated 



% Ci m 0(J2 = X 100 



o 



the relative importance of these alternative pathways. The most notable 

 contribution has been made by Cohen, ^^ who studied the metabolism of 

 glucose-l-C'' by intact cells of E. coli. Whereas utilization of glucose by 

 the direct oxidative pathway would result in preferential conversion of d 

 to CO2 , this would not occur if the glycolytic scheme were operating, since 

 most of the CO2 produced during anaerobic glycolysis arises from the car- 

 boxyl group of pyruvic acid which is derived from C3 or C4 of the original 

 glucose. The results obtained by Cohen are given in Table II. When glucose 

 was oxidized by resting bacteria there was no indication of preferential 

 liberation of CO2 from Ci of glucose. Under conditions of growth, however, 

 an average of 37 % of the Ci was recovered in the liberated CO2 , which is 

 significantly in excess of the value of 23 % which would be obtained if the 

 glucose were converted to pyruvate anaerobically and then metabolized 

 completely. The minimum value for glucose degradation by the oxidative 

 pathway would then be this excess of 14 % and the maximum value would 

 be 37 %. This figure agrees well with the results of later experiments^^ i^ 

 which it was shown that extracts of growing E. coli cells contained sufficient 

 glucose-6-phosphate and 6-phosphogluconate dehydrogenases to account 

 for approximately 40 % of the total metabolism of carbohydrate. When E. 

 coli was infected with T2i'+ bacteriophage, growth was suspended and 

 activity confined exclusively to the synthesis of virus components.^" Under 

 these conditions, the excess of Ci in the liberated CO2 was markedly de- 



«2 D. B. M. Scott and S. S. Cohen, Federation Proc. 11, 284 (1952); Biochem. J. 55, 

 33 (1953). 



