UNIDENTIFIED GROWTH FACTORS IN BREWER'S YEAST: II. SOME CHEMICAL AND PHYSICAL PROPERTIES OF THESE FACTORS

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Abstract
Brewer's yeast contains some unknown growth factors necessary for the normal development of Tribolium confusum. These factors, destroyed by ashing, are organic substances insoluble in ethanol, ether, and benzene. Temperatures as high as 125 °C do not affect their activity. At 150 °C, the growth-promoting effect is decreased. These factors are destroyed by strong acids and slightly affected by strong alkalis. Maximum growth stimulation is obtained between pH 6.0 and 8.8. The presence in water-soluble yeast fraction of a growth-promoting factor is confirmed. The water-insoluble part contains one or many unidentified growth factors.