Enzymes and Fermentation in Yeast Cells 287 



causes TPNH oxidation due to the amination of a-ketogluta- 

 rate, thus supplying TPN and activating the pentose phos- 

 phate cycle. 



REFERENCES 



HoLZER, H. (1953). IV Coll. Ges.physiol. Chem., p. 89. Berlin: Springer. 

 HoLZER, H. (1956). Ergebnisse der Medizinischen Grundlagen- 



forschung, 1, 189. Stuttgart: Thieme. 

 HoLZER, H. (1959). S.C.I. Monograph, No. 3, p. 55. London. 

 HoLZER, H. (1958). VIII Coll. Ges. physiol. Chem., p. 65. Berlin: 



Springer. 

 HoLZER, H., and Freytag-Hilf, R. (1959). Biochem. Z., in press. 

 HoLZER, H., and Holzer, E. (1953). Hoppe-Seylers Z. physiol. Chem., 



292, 232. 

 Holzer, H., Holzer, E., and Schultz, G. (1955). Biochem. Z., 326, 385. 

 Holzer, H., and Schneider, S. (1957). Biochem. Z., 329, 361. 

 Holzer, H., Schultz, G., and Lynen, F., (1956). Biochem. Z., 328, 252. 

 Holzer, H., and Witt, I. (1958a). Biochem. Z., 330, 545. 

 Holzer, H., and Witt, I. (19585). Angew. Chem., 70, 439. 



DISCUSSION 



Coxon: Foulkes (1953, Biochem. J., 54, 323) described a factor which 

 he called the citrate oxidation factor. This was a dialysable material 

 that he got from yeast, having the property that when added to yeast 

 which was oxidizing pyruvate it minimized the quantity of citrate which 

 accumulated. A good deal of analytical work was subsequently done to 

 characterize this factor, and it was found (Whitehouse, M. W., Kent, 

 P. W., Peters, R. A., and Foulkes, E. C. (1954). Biochem. J., 58, 437) 

 that most of the activity could be explained by ammonium ions in the 

 extract — which fits rather well with Prof. Holzer's work. 



Backer: Prof. Holzer, in your Fig. 2 the curves for fructose diphos- 

 phate and triose phosphate were parallel, though of course the triose 

 phosphate values were much lower. In Fig. 6 the fructose diphosphate 

 values went up while triose phosphates did not. I am sure there is a good 

 reason for this but I cannot think of one. 



Holzer : Since in the experiment shown in Fig. 6 the concentrations of 

 fructose diphosphate and triose phosphate are remarkably higher than 

 in the experiment shown in Fig. 2, and since the equilibrium constant 

 of zymohexase depends upon the concentration, it is understandable 

 that triose phosphate — with respect to fructose diphosphate — changes 

 less in Fig. 6 than in Fig. 2. 



Hess: The fructose diphosphate surplus which Prof. Holzer has 

 observed in yeast as a consequence of a lack of DPN can also be demon- 

 strated in ascites tumour cells after addition of glucose, especially if 



