NDLI: Cytochrome P-450TYR Is a Multifunctional Heme-Thiolate Enzyme Catalyzing the Conversion of L-Tyrosine to p-Hydroxyphenylacetaldehyde Oxime in the Biosynthesis of the Cyanogenic Glucoside Dhurrin in Sorghum bicolor (L.) Moench

Content Provider	Journal of Biological Chemistry (JBC)
Author	Sibbesen, Ole Koch, Birgit Halkier, Barbara Ann Møller, Birger Lindberg
Abstract	Cytochrome P-450TYR, which catalyzes the N-hydroxylation of L-tyrosine in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench has recently been isolated (Sibbesen, O., Koch, B., Halkier, B. A., and Møller, B. L. (1994) Proc. Natl. Acad. Sci. U. S. A. 92, 9740-9744). Reconstitution of the enzyme activity in lipid micelles containing cytochrome P-450TYR and NADPH-cytochrome P-450 oxidoreductase demonstrates that cytochrome P-450TYR catalyzes the conversion of L-tyrosine into p-hydroxyphenylacetaldehyde oxime. Earlier studies with microsomes have demonstrated that this conversion involves two N-hydroxylation reactions of which the first produces N-hydroxytyrosine. We propose that the product of the second N-hydroxylation reaction is N,N-dihydroxytyrosine. N,N-dihydroxytyrosine is dehydrated to 2-nitroso-3-(p-hydroxyphenyl) propionic acid which decarboxylates to p-hydroxyphenylacetaldehyde oxime. The dehydration and decarboxylation reactions may proceed non-enzymatically. The E/Z ratio of the p-hydroxyphenylacetaldehyde oxime produced by reconstituted cytochrome P-450TYR is 69:31. Lipid micelles made from L-α-dilauroyl phosphatidylcholine are more than twice as effective in reconstituting cytochrome P-450TYR activity as compared to other lipids. The Km and turnover number of the enzyme is 0.14 mM and 200 min−1, respectively, when assayed in the presence of 15 mM NaCl whereas the values are 0.21 mM and 230 min−1 when assayed in the absence of added salt. The multifunctional nature cytochrome P-450TYR is confirmed by demonstrating that binding of L-tyrosine or N-hydroxytyrosine mutually excludes binding of the other substrate. These results explain why the conversion of tyrosine to p-hydroxyphenylacetaldehyde oxime as earlier reported (Møller, B. L., and Conn, E. E.(1980) J. Biol. Chem. 255, 3049-3056) shows the phenomenon of catalytic facilitation (“channeling”). Cytochrome P-450TYR is the first isolated multifunctional heme-thiolate enzyme from plants. N-Hydroxylases of the cytochrome P-450 type with high substrate specificity have not previously been reported.
Related Links	http://www.jbc.org/content/270/8/3506.abstract
Ending Page	3511
Starting Page	3506
Page Count	6
File Format	HTM / HTML PDF
ISSN	00219258
Journal	Journal of Biological Chemistry (JBC)
Issue Number	8
Volume Number	270
DOI	10.1074/jbc.270.8.3506
e-ISSN	1083351X
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	1995-02-24
Access Restriction	Open
Subject Keyword	Enzymology
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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Isolation of the heme-thiolate enzyme cytochrome P-450TYR, which catalyzes the committed step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench.

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Isolation of the heme-thiolate enzyme cytochrome P-450TYR, which catalyzes the committed step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench.

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2-nitro-3-(p-hydroxyphenyl)propionate and aci-1-nitro-2-(p-hydroxyphenyl)ethane, two intermediates in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench.

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Cytochrome P-450TYR Is a Multifunctional Heme-Thiolate Enzyme Catalyzing the Conversion of L-Tyrosine to p-Hydroxyphenylacetaldehyde Oxime in the Biosynthesis of the Cyanogenic Glucoside Dhurrin in Sorghum bicolor (L.) Moench

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Cytochrome P-450TYR Is a Multifunctional Heme-Thiolate Enzyme Catalyzing the Conversion of L-Tyrosine to p-Hydroxyphenylacetaldehyde Oxime in the Biosynthesis of the Cyanogenic Glucoside Dhurrin in Sorghum bicolor (L.) Moench