The regulation of respiration during the assimilation of nitrogen in Torulopsis utilis

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Abstract
Nitrogen-deficient cultures of food yeast, T. utilis, suspended under aerobic conditions in a carbohydrate-free medium, were shown to respond rapidly to the addition of ammonium phosphate by increasing their rate of O2 uptake to 2 or 3 times the previous level. Their CO2 output is also increased but the R.Q. falls from 1.05 to about 0.85. This increase in respiration is accompanied by the assimilation of ammonia and a close quantitative relationship between these metabolic processes can be demonstrated. N deficiency can be induced by culture of the yeast in a high-carbohydrate, N-free solution, and its onset is associated with a marked increase in the level of stored carbohydrate and other materials within the yeast, and with an increase in the protein content at the expense of the soluble N compounds. This gives a greater capacity for N assimilation upon treatment with ammonia. The assimilated nitrogen appears mainly as glutamine, alanine, glutamic acid and, later, as protein. These syntheses are accompanied by the breakdown of stored carbohydrates, mainly glycogen and mannan, and of fats. 2:4-Dinitrophenol (DNP) has been found to inhibit the assimilation of nitrogen and to cause increased oxygen uptake and carbohydrate breakdown. At higher concentrations of DNP oxygen uptake also is inhibited and fermentation reactions predominate. These results are discussed with special reference to the problem of the regulation of respiration and glycolysis within the cell. It is suggested that the assimilation of nitrogen may increase the rate of carbohydrate breakdown and of respiration in three ways: the synthesis of amide and peptide bonds may lower the level of high-energy phosphate compounds, the diversion of electrons for reductive amination reactions may alter the oxidation -reduction conditions within the cell, and the synthesis of amino acids and proteins may make large demands upon the organic acids produced in the course of glycolysis and respiration.