Studies on the Biochemistry of Tetrahymena

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Abstract
Under certain defined conditions, the optimum concs. of essential amino acids were determined for the ciliated protozoan Tetrahymena. Availability of the optical isomers was investigated. Quantitative results indicate that both the L- and D-isomers of lysine, methionine, threonine and tryptophane are active. Both isomers of isoleucine are active in the presence of serine. The unnatural isomers of leucine, phenylala-nine and valine are inhibitory. High levels of L-isoleucine are required in the absence of serine and the racemic mixture is completely inhibitory. Serine functions as an antagonist to the inhibition exhibited by 9 of the essential amino acids. In the absence of serine the growth rate was invariably low and the maximum yield usually reduced. High levels of threonine can substitute for serine for release of inhibition but threonine is not a growth rate stimulator. Comparisons are made between the data in the literature on vertebrates and those reported here on Tetrahymena.
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