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Yeast's primitive urea

Ammonium induces yeast to excrete amino acids. HESS/PLOS

Yeast cells pee out amino acids to avoid ammonium toxicity, say David Hess (Princeton University, Princeton, NJ) and colleagues.

The group was initially interested in the effect of potassium, not ammonium. But their microarray data suggested that low potassium is harmful to yeast because ammonium—a similarly sized and charged ion—seeps in through the battery of induced potassium channels.

The yeast protect themselves from the intracellular ammonium by incorporating it into amino acids that they then secrete into the medium. Export seems to be through passive channels that also take up amino acids. The export may help natural yeast strains survive on ammonium-rich rotting vegetation (in which the external source of amino acids is probably also handy later on). Standard laboratory media have very high potassium levels that apparently masked ammonium's toxic effects on yeast before now.

The initial cellular response to high ammonium—converting it to glutamine or glutamate—is evolutionarily conserved. Since glutamine is a neurotoxin, however, mammals must further convert the excess amino acids to urea. "The root cause of ammonium toxicity is not understood in mammalian systems," says Hess. At least now, he says, "we can use yeast as a model."

Reference:

Hess, D.C., et al. 2006. PLoS Biol. doi:10.1371/journal.pbio.0040351.

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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This Article Full Text (PDF, 845K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Social Bookmarking                            What's this?