Featured Research

from universities, journals, and other organizations

Potassium Limitation, Ammonium Toxicity And Amino Acid Excretion In Yeast

Date:
October 19, 2006
Source:
Public Library of Science
Summary:
An amino acid excretion mechanism is identified in yeast. This stress response helps purge excess nitrogen when ammonium ion toxicity is encountered, presumed to leak through potassium channels, in potassium-limiting conditions.

By applying systems-level biology to yeast cells growing in steady-state potassium limited chemostats, pictured above, the authors uncovered ammonium toxicity in yeast.
Credit: Image M. Dunham / Courtesy of PloS Biology

As a single-celled eukaryote organism, the yeast strain S. cerevisiae has some limitations in terms of how it can be used as a model for more complex multicellular eukaryotes. However, in an article published online this week in the open access journal PLoS Biology, David Hess, David Botstein, and colleagues demonstrate that a stress response to ammonium toxicity (linked with limited potassium) in yeast is dealt with by amino acid excretion and is likely to be a yeast equivalent of urea excreted by mammals in urine.

Using microarrays, the authors found that, in potassium-limiting conditions, many genes involved in nitrogen metabolism showed altered activity compared with unstressed cells. These expression patterns suggested that some attempt was being made by the cell to deal with a toxic influx of nitrogen in the cell--intriguing as nitrogen toxicity was thought to be limited to multicellular organisms.

Using a chemostat, the authors monitored the responses of cells exposed to different levels of ammonium and potassium. In low potassium, cell numbers decreased dramatically (suggesting a toxic effect of ammonium when potassium is limited). Indeed, using alternate nitrogen-rich sources in place of ammonium, the authors saw that this was not a general nitrogen response, but one specific to ammonium. Tests across different yeast strains found this to be not a quirk on one strain of S. cerevisiae. Further as a metabolic fingerprint of this adverse reaction to ammonium, the researchers observed high levels of amino acids in the cellular environment of these potassium-limited cells, as measured by liquid chromatography tandem mass spectrometry in collaboration with the Rabinowitz lab at Princeton.

To investigate further the link between potassium concentration and ammonium toxicity, the authors hypothesized that ammonium might leak into cells through potassium channels when they are not occupied by potassium. Indeed, in an engineered strain in which ammonium influx could be increased without stimulating innate ammonium concentration regulatory mechanisms, the cells engineered to let in more ammonium showed greater mortality even in high potassium concentration, supporting the idea that ammonium is the root of the problem. Also in these engineered cells, growth was limited even though potassium was not, and again, a high level of amino acid excretion was seen.

It seems, therefore, that S. cerevisiae experiences ammonium toxicity under potassium-deprived conditions and that it uses a primitive detoxification system involving the production and excretion of amino acids in an attempt to deal with it.

Citation: Hess DC, Lu W, Rabinowitz JD, Botstein D (2006) Ammonium toxicity and potassium limitation in yeast. PLoS Biol 4(11): e351. DOI: 10.1371/journal.pbio.0040351.


Story Source:

The above story is based on materials provided by Public Library of Science. Note: Materials may be edited for content and length.


Cite This Page:

Public Library of Science. "Potassium Limitation, Ammonium Toxicity And Amino Acid Excretion In Yeast." ScienceDaily. ScienceDaily, 19 October 2006. <www.sciencedaily.com/releases/2006/10/061017085121.htm>.
Public Library of Science. (2006, October 19). Potassium Limitation, Ammonium Toxicity And Amino Acid Excretion In Yeast. ScienceDaily. Retrieved August 31, 2014 from www.sciencedaily.com/releases/2006/10/061017085121.htm
Public Library of Science. "Potassium Limitation, Ammonium Toxicity And Amino Acid Excretion In Yeast." ScienceDaily. www.sciencedaily.com/releases/2006/10/061017085121.htm (accessed August 31, 2014).

Share This




More Plants & Animals News

Sunday, August 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

We've Got Mites Living In Our Faces And So Do You

We've Got Mites Living In Our Faces And So Do You

Newsy (Aug. 30, 2014) A new study suggests 100 percent of adult humans (those over 18 years of age) have Demodex mites living in their faces. Video provided by Newsy
Powered by NewsLook.com
Experimental Ebola Drug ZMapp Cures Lab Monkeys Of Disease

Experimental Ebola Drug ZMapp Cures Lab Monkeys Of Disease

Newsy (Aug. 29, 2014) In a new study, a promising experimental treatment for Ebola managed to cure a group of infected macaque monkeys. Video provided by Newsy
Powered by NewsLook.com
Killer Amoeba Found in Louisiana Water System

Killer Amoeba Found in Louisiana Water System

AP (Aug. 28, 2014) State health officials say testing has confirmed the presence of a killer amoeba in a water system serving three St. John the Baptist Parish towns. (Aug. 28) Video provided by AP
Powered by NewsLook.com
Raw: Australian Sheep Gets Long Overdue Haircut

Raw: Australian Sheep Gets Long Overdue Haircut

AP (Aug. 28, 2014) Hoping to break the record for world's wooliest, Shaun the sheep came up 10 pounds shy with his fleece weighing over 50 pounds after being shorn for the first time in years. (Aug. 28) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins