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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Møller, Birger Lindberg Bak, Søren Trompetter, Inga Jenrich, Roland Olsen, Carl Erik Piotrowski, Markus |
| Description | Author Affiliation: Jenrich R ( Department of Plant Physiology, Ruhr-Universität Bochum, 44801 Bochum, Germany.); |
| Abstract | Members of the nitrilase 4 (NIT4) family of higher plants catalyze the conversion of beta-cyanoalanine to aspartic acid and asparagine, a key step in cyanide detoxification. Grasses (Poaceae) possess two different NIT4 homologs (NIT4A and NIT4B), but none of the recombinant Poaceae enzymes analyzed showed activity with beta-cyanoalanine, whereas protein extracts of the same plants clearly posses this activity. Sorghum bicolor contains three NIT4 isoforms SbNIT4A, SbNIT4B1, and SbNIT4B2. Individually, each isoform does not possess enzymatic activity whereas the heteromeric complexes SbNIT4A/B1 and SbNIT4A/B2 hydrolyze beta-cyanoalanine with high activity. In addition, the SbNIT4A/B2 complex accepts additional substrates, the best being 4-hydroxyphenylacetonitrile. Corresponding NIT4A and NIT4B isoforms from other Poaceae species can functionally complement the sorghum isoforms in these complexes. Site-specific mutagenesis of the active site cysteine residue demonstrates that hydrolysis of beta-cyanoalanine is catalyzed by the NIT4A isoform in both complexes whereas hydrolysis of 4-hydroxyphenylacetonitrile occurs at the NIT4B2 isoform. 4-Hydroxyphenylacetonitrile was shown to be an in vitro breakdown product of the cyanogenic glycoside dhurrin, a main constituent in S. bicolor. The results indicate that the SbNIT4A/B2 heterocomplex plays a key role in an endogenous turnover of dhurrin proceeding via 4-hydroxyphenylacetonitrile and thereby avoiding release of toxic hydrogen cyanide. The operation of this pathway would enable plants to use cyanogenic glycosides as transportable and remobilizable nitrogenous storage compounds. Through combinatorial biochemistry and neofunctionalizations, the small family of nitrilases has gained diverse biological functions in nitrile metabolism. |
| ISSN | 00278424 |
| e-ISSN | 10916490 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Issue Number | 47 |
| Volume Number | 104 |
| Language | English |
| Publisher | National Academy of Sciences |
| Publisher Date | 2007-11-01 |
| Publisher Place | United States |
| Access Restriction | Open |
| Subject Keyword | Aminohydrolases Genetics Metabolism Evolution, Molecular Nitriles Poaceae Enzymology Alanine Analogs & Derivatives Isolation & Purification Binding Sites Cyanides Chemistry Toxicity Kinetics Molecular Structure Phylogeny Drug Effects Protein Binding Recombinant Proteins Substrate Specificity Research Support, Non-U.S. Gov't Multidisciplinary |
| Content Type | Text |
| Resource Type | Article |
| Subject | Multidisciplinary |
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