The effect of insulin upon the rate of fermentation of glucose by yeast.

Abstract

The possible effect of insulin upon the rate of fermentation of glucose by yeast was studied. Five samples of insulin were tested in twelve experiments. The insulin used was supplied by Eli Lilly and Co., to whom we are indebted for this courtesy. Merck's highest purity glucose was used. The yeast employed was fresh baker's (Fleischmann's) yeast. The same volume of a solution of glucose was allowed to stand with measured quantities of yeast suspension at about 35° C, with and without the addition of insulin. Portions of the solutions were withdrawn from time to time and determinations made of the amount of sugar remaining as the action of the yeast proceeded. In some of the experiments a phosphate buffer solution was added. A summary of two out of the twelve experiments follows.

Starting with 100 cc. of 1 per cent glucose, and using 10 cc. of a 10 per cent suspension of yeast and 10 units of insulin in 10 cc. of water and no buffer, it was found that the sugar fell in three and a half hours from 0.80 gm. per 100 cc. of the original solution to 0.38 gm., in the solution without insulin, and from 0.81 to 0.37 gm., in the solution with insulin. In another case, starting with 50 cc. of 5 per cent glucose, using 10 cc. of 10 per cent yeast suspension, 40 units of insulin and 10 cc. of a phosphate buffer solution, the sugar fell after nineteen hours from 2.54 to 1.63 gm. per 100 cc. of the original solution, in the flask containing no insulin, and from 2.6 to 1.64 gm. where insulin was present.

These results are representative of seven experiments carried out with four samples of insulin, one of which contained no preservative and the others either toluene or trikresol.