title: Metabolism of homocysteine-thiolactone in plants.
abstract: Editing of the amino acid homocysteine (Hcy) by certain aminoacyl-tRNA synthetases results in the formation of an intramolecular thioester, Hcy-thiolactone. Here we show that the plant yellow lupin, Lupinus luteus, has the ability to synthesize Hcy-thiolactone. The inhibition of methylation of Hcy to methionine by the anitifolate drug aminopterin results in greatly enhanced synthesis of Hcy-thiolactone by L. luteus plants. Methionine inhibits the synthesis of Hcy-thiolactone in L. luteus, suggesting involvement of methionyl-tRNA synthetase. Consistent with this suggestion is our finding that the plant Oryza sativa methionyl-tRNA synthetase, expressed in Escherichia coli, catalyzes conversion of Hcy to Hcy-thiolactone. We also show that Hcy is a component of L. luteus proteins, most likely due to facile reaction of Hcy-thiolactone with protein amino groups. In addition, L. luteus possesses constitutively expressed, highly specific Hcy-thiolactone-hydrolyzing enzyme. Thus, Hcy-thiolactone and Hcy bound to protein by an amide (or peptide) linkage (Hcy-N-protein) are significant components of plant Hcy metabolism.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Medicine and Dentistry of New Jersey (UMDNJ)-New Jersey Medical School, International Center for Public Health, Newark, New Jersey 07101, USA. jakubows@umdnj.edu
authors.forename: Hieronim
authors.initials: H
authors.lastname: Jakubowski
authors.forename: Andrzej
authors.initials: A
authors.lastname: Guranowski
mesh_terms: D000630:Aminopterin / Q000494:pharmacology; D002412:Cations; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004926:Escherichia coli / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000494:pharmacology; D006710:Homocysteine / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D007783:Lactones / Q000737:chemistry*; D031297:Lupinus / Q000201:enzymology; D008956:Models, Chemical; D012275:Oryza / Q000201:enzymology; D012639:Seeds / Q000378:metabolism; D013053:Spectrophotometry; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: D002412:Cations; D005493:Folic Acid Antagonists; D007783:Lactones; D006710:Homocysteine; D000630:Aminopterin