Accurate Measurement of the in vivo Ammonium Concentration in Saccharomyces cerevisiae.

Ammonium (NH₄⁺) is the most common N-source for yeast fermentations, and N-limitation is frequently applied to reduce growth and increase product yields. While there is significant molecular knowledge on NH₄⁺ transport and assimilation, there have been few attempts to measure the in vivo concentration of this metabolite. In this article, we present a sensitive and accurate analytical method to quantify the in vivo intracellular ammonium concentration in Saccharomyces cerevisiae based on standard rapid sampling and metabolomics techniques.

How to obtain true and accurate rate-values.

In metabolic flux calculations, the uptake and secretion rates (for substrate, O(2), CO(2), growth, (by)-products) are essential to arrive at correct calculated fluxes. Surprisingly, a lot of research has been published on the methods of flux calculations, but much less attention has been spent on the methods to obtain accurate and true uptake and secretion rates which are used as input. Therefore, this contribution focuses on.