BIOSYNTHETIC FORMATION OF HIGHER ALCOHOLS BY YEAST. DEPENDENCE ON THE NITROGENOUS NUTRIENT LEVEL OF THE MEDIUM

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Abstract
In previous investigations it has been shown that in batch fermentations the yield of higher alcohols formed biosynthetically (in the sense that yeast synthesizes the carbon skeletons needed) is mainly negatively correlated with the intial level of nitrogenous nutrients in the medium. The validity of this relationship has been established with different nitrogen sources and sugars, and at different sugar concentrations. Its causes have been studied in simple systems, using single, rapidly-absorbed nitrogen sources, usually ammonium salts. Under such conditions it is the amount, rather than the concentration, of nitrogen source that is of importance. Yields of higher alcohols per unit weight sugar consumed are practically identical at varying nitrogen levels as long as nitrogen is available in the medium, but they increase sharply after nitrogen exhaustion, by a factor of about 2–3. However, if allowance is made for the production of valine, leucine, and isoleucine during the period when nitrogen is present, there is no rise in the total production of carbon skeletons along these pathways after the nitrogen is exhausted. On the contrary, the yields of valine-isobutanol and isoleucine-2-methylbutanol skeletons per unit weight of sugar are appreciably reduced in the absence of nitrogen, whereas the yields of leucine-3-methylbutanol skeletons are nearly unchanged.

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