Free Amino Acids in Serine-Antagonized Cells of Tetrahymena pyriformis

Abstract

Growth inhibition of Tetrahymena pyriformis by L-serine in a chemically defined medium was reversed by L-arginine in a manner which resembled competitive antagonism. Composition of the free amino acid pools from cells grown in either a balanced amino acid mixture or a mixture with serine concentrations which inhibited growth suggested an antagonism by serine with energy-yielding reactions. Growth in media with excess serine resulted in the accumulation of higher concentrations of free cellular amino acids and an apparent increase in the rate of conversion of arginine to ornithine, as compared with growth in the balanced medium. The results suggested that serine or a metabolic product of serine interferes with the formation of pyruvic acid. In the presence of high levels of serine, arginine appeared to be metabolized more rapidly and to be spared when alanine, aspartic acid, or glutamic acid was added to the unbalanced medium.

15N investigation into the effect of a pollutant on the nitrogen metabolism of Tetrahymena pyriformis as a model for environmental medical research.

“…The amino acids in the nutritional medium showed no differences. Ornithine and glutamic acid were detected, which conforms with the findings of other authors (14,46). The high 15N enrichment of glutamic acid may point out that this compound is a secretion whose purpose is to release ammonia from the cell.…”

“…With Tetrahymena pyriformis, conventional toxicity tests are usual and are performed using certain complex media (6,(10)(11)(12)(13). In this investigation a combination of the chemically defined media (29) regarding salts, trace salts, and vitamins and of certain amino acid composition (14) was chosen to ensure defined conditions for reproducible isotopic and mass spectrometric analyses. Our working hypothesis was that the impact of a pollutant should be reflected in changes in both the amount and the 15N abundance ofnitrogen in the various pools.…”

“…But arginine plays a key role in various physiological processes (38). In Tetrahymena pyriformis, however, the two-step hydrolytic cleavage results in ammonia formation and provides energy (14,39). The higher arginine consumption is probably due to higher energy requirements under toluene stress.…”

“…The purpose of this investigation was to identify metabolic changes in normal cell metabolism (biological effect monitoring), namely, at the level of amino acid and protein metabolism. The Tetrahymena cells generally require 11 essential amino acids, including arginine (14). Because these eukaryotes lack the urea cycle present in mammals, the final product of nitrogen metabolism is ammonia (15,16).…”