title: Evidence for several cysteine transport mechanisms in the mitochondrial membranes of Arabidopsis thaliana.
abstract: Cysteine is essential for many mitochondrial processes in plants, including translation, iron-sulfur cluster biogenesis and cyanide detoxification. Its biosynthesis is carried out by serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL) which can be found in the cytosol, plastids and mitochondria. Mutants lacking one compartment-specific OAS-TL isoform show viable phenotypes, leading to the hypothesis that the organellar membranes are permeable to substrates and products of the cysteine biosynthetic pathway. In this report, we show that exogenouslly supplied [(35)S]cysteine accumulates in the mitochondrial fraction and is taken up into isolated mitochondria for in organello protein synthesis. Analysis of cysteine uptake by isolated mitochondria and mitoplasts indicates that cysteine is transported by multiple facilitated mechanisms that operate in a concentration gradient-dependent manner. In addition, cysteine uptake is dependent mainly on the ΔpH across the inner membrane. The rates of mitochondrial cysteine transport can be mildly altered by specific metabolites in the cyanide detoxification-linked sulfide oxidation, but not by most substrates and products of the cysteine biosynthetic pathway. Based on these results, we propose that the transport of cysteine plays a pivotal role in regulating cellular cysteine biosynthesis as well as modulating the availability of sulfur for mitochondrial metabolism.
authors.affiliation: Centre for Organismal Studies (COS) Heidelberg, Im Neuenheimer Feld 360, University of Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: Chun Pong
authors.initials: CP
authors.lastname: Lee
authors.forename: Markus
authors.initials: M
authors.lastname: Wirtz
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hell
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D003545:Cysteine / Q000378:metabolism*; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects; D013460:Sulfur Isotopes; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D013460:Sulfur Isotopes; D014475:Uncoupling Agents; D003545:Cysteine
keywords: Arabidopsis thaliana; Cysteine biosynthesis and catabolism; Cysteine transport; Mitochondria; Proton gradient; Sulfur assimilation