期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2001
卷号：98
期号：26
页码：14843-14848
DOI：10.1073/pnas.011578198
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The first step in the biosynthetic pathway of vitamin C in plants is the formation, at the level of sugar nucleotide, of L-galactosyl residues, catalyzed by a largely unknown GDP-D-mannose 3",5"-epimerase. By using combined conventional biochemical and mass spectrometry methods, we obtained a highly purified preparation of GDP-D-mannose 3",5"-epimerase from an Arabidopsis thaliana cell suspension. The native enzyme is an 84-kDa dimer, composed of two apparently identical subunits. In-gel tryptic digestion of the enzyme subunit, followed by peptide sequencing and a BLAST search, led to the identification of the epimerase gene. The closest homolog of the plant epimerase is the BlmG gene product of Streptomyces sp., a putative NDP-D-mannose 5"-epimerase. The plant GDP-D-mannose 3",5"-epimerase is, to our knowledge, a novel member of the extended short-chain dehydrogenase/reductase family. The enzyme was cloned and expressed in Escherichia coli cells.
