Free intracellular amino acid pools during autonomous oscillations in Saccharomyces cerevisiae

Abstract

In the present work dynamic changes of free intracellular amino acid pools during autonomous oscillations of Saccharomyces cerevisiae were quantified in glucose-limited continuous cultivations. At a dilution rate of D = 0.22 h(-1) cyclic changes with a period of 120 min were found for many variables such as carbon dioxide production rate, dissolved oxygen, pH, biomass content, and various metabolite concentrations. On the basis of the observed dynamic patterns, free intracellular amino acids were classified to show oscillatory, stationary, or chaotic behavior. Amino acid pools such as serine, alanine, valine, leucine, or lysine were subjected to clear oscillations with a frequency of 120 min, identical to that of other described cultivation variables, indicating that there is a direct correlation between the periodic changes of amino acid concentrations and the metabolic oscillations on the cellular level. The oscillations of these amino acids were unequally phase-delayed and had different amplitudes of oscillation. Accordingly, they exhibited different patterns in phase plane plots vs. intracellular trehalose. Despite the complex and marked metabolic changes during oscillation, selected intracellular amino acids such as histidine, threonine, isoleucine, or arginine remained about constant. Concentrations of glutamate and glutamine showed a chaotic behavior. However, the ratio of glutamate to glutamine concentration was found to be oscillatory, with a period of 60 min and a corresponding figure eight-shaped pattern in a plot vs. trehalose concentration. Considering the described diversity, it can be concluded that the observed periodic changes are neither just the consequence of low or high rates of protein biosynthesis/degradation nor correlated to changing cell volumes during oscillation. The ratio between doubling time (189 min) and period of oscillation of intracellular amino acids (120 min) was 1:6. The fact that there is a close relationship between doubling time and period of oscillation underlines that the described autonomous oscillations are cell-cycle-associated.

Suppression of metabolic defects of yeast isocitrate dehydrogenase and aconitase mutants by loss of citrate synthase

“…The level of glutamate was the highest among metabolites analyzed, consistent with previous reports that this is an abundant free amino acid in yeast cells [26,27]. In contrast, the level of aspartate was more similar to those of abundant TCA cycle metabolites.…”

“…In general, levels of tricarboxylic acid cycle intermediates were slightly lower (~50%) in glucose-grown cells as compared with galactose-grown cells; for the parental strain, metabolite levels were comparable to those reported in other analyses of glucose-grown yeast strains [20,27,28]. However, compared to the parental strain, relative levels of metabolites for mutant strains grown with glucose were very similar to those observed with galactose.…”

Role of phosphatidylserine synthase in shaping the phospholipidome of Candida albicans

“…4B) were obtained. Interestingly, the intracellular concentration of serine in S. cerevisiae has been estimated to be around 2 mM on average (Hans, Heinzle and Wittmann 2003), which fits well with the K m for serine. These assays were performed on the crude 27 000 × g membranes in order to determine their kinetics within native membranes.…”

Glutamine-dependent NAD+ Synthetase

“…, K m ϭ 40 mM) reveals that the K m -Gln is greater than twice the concentration of glutamine observed in vivo (16). Thus, it would be reasonable to say that binding of NaAD ϩ to Qns1-Gln in the absence of ATP causes Gln to dissociate.…”