II. Reaction of Fructose with Phosphates in Presence of Yeast-Juice.
Although, as has been pointed out (p. [42]), glucose, mannose, and fructose all react with phosphate in a similar manner in presence of yeast-juice, there are nevertheless certain quantitative differences between the behaviour of glucose and mannose on the one hand, and fructose on the other, which appear to be of considerable importance. Fructose differs from the other two fermentable hexoses in two particulars: (1) the optimum concentration of phosphate is much greater; (2) the maximum rate of fermentation attainable is much higher [Harden and Young, [1908, 2]; [1909]].
These points are clearly illustrated by the following results, which all refer to 10 c.c. of yeast-juice, and show that the optimum concentration of phosphate for the fermentation of fructose is from 1·5 to 10 times that of glucose, and that the maximum rate of fermentation for fructose in presence of phosphate is 2 to 6 times that of glucose.
| Sugar in Grams. | Total Volume. | Optimum Volume of 0·6 Molar Phosphate in c.c. | Maximum Rate in Cubic Centimetres of CO2 per Five minutes. | ||
|---|---|---|---|---|---|
| Glucose. | Fructose. | Glucose. | Fructose. | ||
| 2 | 35 | 2 | 5 | 7·5 | 32·2 |
| 4 | 50 | 1 | 10 | 5·4 | 28·4 |
| 1·6 | 23 | 2 | 5 | 8 | 17 |
| 1 | 25 | 1·75 | 5 | 5·2 | 25·9 |
| 2 | 25 | 5 | 7·5 | 16·2 | 31·2 |
| 2 | 20 | 2 | 3·5 | 7·9 | 22·6 |
| 2 | 22·5 | 0·75 | 2 | 3·4 | 22·2 |
It is interesting to note that the two high rates, 32·2 and 31·2 c.c. per five minutes, are equal to about half the rate obtainable with an amount of living yeast corresponding to 10 c.c. of yeast-juice, assuming that about 16 to 20 grams of yeast are required to yield this volume of juice, and that this amount of yeast would give about 56 to 70 c.c. of carbon dioxide per five minutes at 25°, which has been found experimentally to be about the rate obtainable with the top yeast employed for these experiments.