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

Journal Article · Tue Jan 15 00:00:00 EST 1991 · Proceedings of the National Academy of Sciences of the United States of America; (United States)

DOI:https://doi.org/10.1073/pnas.88.2.487· OSTI ID:5016492

Halkier, B A; Lykkesfeldt, J; Moller, B L ^[1]

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1. Royal Veterinary and Agricultural Univ., Copenhagen (Denmark)

The biosynthetic pathway for the cyanogenic glucoside dhurrin derived from tyrosine has been studied in vitro by using ({sup 18}O)oxygen and a microsomal enzyme system obtained from etiolated sorghum seedlings. The products formed were purified by HPLC and TLC, and the incorporation of ({sup 18}O)oxygen was monitored by mass spectrometry. In the presence of NADPH and ({sup 18}O)dioxygen, L-tyrosine is converted to (E)- and (Z)-p-hydroxyphenylacetaldhyde oxime with quantitative incorporation of an ({sup 18}O)oxygen atom into the oxime function. These data demonstrate that the conversion of N-hydroxytyrosine to p-hydroxyphenylacetaldehyde oxime involves additional N-hydroxylation and N-oxidation reactions giving rise to the formation of 2-nitro-3-(p-hydroxyphenyl)propionate, which by decarboxylation produces aci-1-nitro-2-(p-hydroxyphenyl)ethane. Both compounds are additional intermediates in the pathway. The two ({sup 18}O)oxygen atoms introduced by the N-hydroxylations are enzymatically distinguishable as demonstrated by the specific loss of the oxygen atom introduced by the first N-hydroxylation reaction in the subsequent conversion of aci-1-nitro-2-(p-hydroxyphenyl)ethane to (E)-p-hydroxyphenylacetaldehyde oxime. A high flux of intermediates through the microsomal enzyme system is obtained with N-hydroxytyrosine as a substrate. This renders the conversion of the aci-nitro compound rate limiting and results in its release from the active site of the enzyme system and accumulation of the tautomeric nitro compound.

• OSTI ID: 5016492
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (United States), Vol. 88:2; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
GLYCOSIDES
BIOLOGICAL PATHWAYS
PROPIONIC ACID
BIOCHEMICAL REACTION KINETICS
TYROSINE
HYDROXYLATION
MASS SPECTRA
MICROSOMES
OXYGEN 18
REACTION INTERMEDIATES
SEEDLINGS
SORGHUM
AMINO ACIDS
CARBOHYDRATES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CEREALS
EVEN-EVEN NUCLEI
GRAMINEAE
HYDROXY ACIDS
ISOTOPES
KINETICS
LIGHT NUCLEI
LILIOPSIDA
MAGNOLIOPHYTA
MONOCARBOXYLIC ACIDS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN ISOTOPES
PLANTS
REACTION KINETICS
RIBOSOMES
SPECTRA
STABLE ISOTOPES
550201* - Biochemistry- Tracer Techniques