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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

beta-Cyano-alanine synthase (CAS; EC 4.4.1.9) plays an important role in cyanide metabolism in plants. Although the enzymatic activity of beta-cyano-Ala synthase has been detected in a variety of plants, no cDNA or gene has been identified so far. We hypothesized that the mitochondrial cysteine synthase (CS; EC 4.2.99. 8) isoform, Bsas3, could actually be identical to CAS in spinach (Spinacia oleracea) and Arabidopsis. An Arabidopsis expressed sequence tag database was searched for putative Bsas3 homologs and four new CS-like isoforms, ARAth;Bsas1;1, ARAth;Bsas3;1, ARAth;Bsas4;1, and ARAth;Bsas4;2, were identified in the process. ARAth;Bsas3;1 protein was homologous to the mitochondrial SPIol;Bsas3;1 isoform from spinach, whereas ARAth;Bsas4;1 and ARAth;Bsas4;2 proteins defined a new class within the CS-like proteins family. In contrast to spinach SPIol;Bsas1;1 and SPIol;Bsas2;1 recombinant proteins, spinach SPIol;Bsas3;1 and Arabidopsis ARAth;Bsas3;1 recombinant proteins exhibited preferred substrate specificities for the CAS reaction rather than for the CS reaction, which identified these Bsas3 isoforms as CAS. Immunoblot studies supported this conclusion. This is the first report of the identification of CAS synthase-encoding cDNAs in a living organism. A new nomenclature for CS-like proteins in plants is also proposed.
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PMID:beta-Cyanoalanine synthase is a mitochondrial cysteine synthase-like protein in spinach and Arabidopsis. 1088 65

Beta-cyanoalanine synthase (CAS, L-3-cyanoalanine synthase; EC 4.4.1.9) is the most important enzyme in cyanide metabolism. In addition to CAS, cysteine synthase (CS, EC 4.2.99.8) possesses CAS activity. To explore the physiological significance of cyanide metabolism, we isolated the cDNA clones corresponding to purified CAS (designated PCAS-1 and PCAS-2) and CS (designated PCS-1 and PCS-2) from potato using the information of these amino acid sequences. The recombinant proteins of PCS-1, PCS-2 and PCAS-1 catalyzed both CAS and CS reactions, although the ratios between CAS and CS activity were remarkably different. PCAS-1 preferred the substrates for the CAS reaction to the substrates for the CS reaction. From the kinetic characters and homology of amino acid sequences with known CS-like proteins, PCS-1, PCS-2 and PCAS-1 were identified as cytosolic CS, plastidic CS and mitochondrial CAS, respectively. The highest level of CAS activity, CAS protein and its mRNA were detected in potato buds. Stimulation of CAS activity and protein accumulation by ethylene without the concomitant increase of its mRNA suggested that ethylene induces CAS protein accumulation at the post-transcriptional level.
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PMID:Beta-cyanoalanine synthase and cysteine synthase from potato: molecular cloning, biochemical characterization, and spatial and hormonal regulation. 1157 29