SUCROSE INVERSION BY BAKERS' YEAST AS A FUNCTION OF TEMPERATURE.
Inversion of sucrose by bakers' yeast follows the same course as inversion catalyzed by yeast invertase. Rate of inversion increases exponentially with temperature; the temperature characteristic in the Arrhenius equation is 10,700 below 13-17 degrees C., and 8,300 above that temperature. Temperature inactivation occurs above 40 degrees C. The effects of temperature upon rate of inversion were the same using Fleischmann's yeast cake, the same yeast killed with toluene, and a pure strain (G. M. No. 21062) of bakers' yeast. The last differed from the other two only in the fact that its critical temperature was 13 degrees C. as compared with 17 degrees C. for the others. The catalytic inversion is associated with enzyme activity inside the cell, not in the medium, and is independent of any vital processes inside the cell such as respiration and fermentation. Since invertase activity is the same inside the cell as it is after extraction, it appears possible to relate the temperature characteristics for physiological processes to the catalytic chemical systems which determine their rate. At least two enzymes are capable of inverting sucrose in the yeast cell. The familiar yeast invertase (micro = 10,700) is active below 13-17 degrees C. while a second enzyme (M = 8,300) plays the dominant role above that temperature.
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Laboratory of Physiology and Biochemistry, Massachusetts Institute of Technology, Cambridge.