The biosynthesis of cyanogenic glucosides in higher plants. Channeling of intermediates in dhurrin biosynthesis by a microsomal system from Sorghum bicolor (Linn) Moench

The biosynthetic pathway for the cyanogenic glucoside, dhurrin, involves the following intermediates: L-tyrosine, N-hydroxytyrosine, p-hydroxyphenylacetaldoxime, p-hydroxyphenylacetonitrile, and p-hydroxymandelonitrile. N-Hydroxytyrosine and p-hydroxy-phenylacetonitrile produced from L-tyrosine by m...

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Bibliographic Details
Published in:The Journal of biological chemistry 1980-04, Vol.255 (7), p.3049-3056
Main Authors: Møller, B L, Conn, E E
Format: Article
Language:English
Subjects:
Carbon Radioisotopes
Glucosides - biosynthesis
Glycosides - biosynthesis
Isotope Labeling
Kinetics
Microsomes - metabolism
Nitriles - biosynthesis
Nitriles - metabolism
Oximes - metabolism
Plants - metabolism
Tritium
Tyrosine - metabolism
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Summary:The biosynthetic pathway for the cyanogenic glucoside, dhurrin, involves the following intermediates: L-tyrosine, N-hydroxytyrosine, p-hydroxyphenylacetaldoxime, p-hydroxyphenylacetonitrile, and p-hydroxymandelonitrile. N-Hydroxytyrosine and p-hydroxy-phenylacetonitrile produced from L-tyrosine by microsomes from seedlings of Sorghum bicolor are utilized more effectively as substrates than exogenously added N-hydroxytyrosine and p-hydroxyphenylacetonitrile. The minimum values for the channeling ratios are 25 for N-hydroxytyrosine and 115 for p-hydroxyphenylacetonitrile. On the other hand, p-hydroxyphenylacetaldoxime produced internally exchanges readily with exogenously added p-hydroxyphenylacetaldoxime. These results indicate that the biosynthetic pathway is catalyzed by two mutienzyme complexes or by two multifunctional proteins and explain why the rate of the overall sequential reaction starting from L-tyrosine is greater than the rates of reaction initiated later in the sequence with the known intermediates N-hydroxytyrosine and p-hydroxyphenylacetonitrile. Attempts to cross-link chemically the last enzyme in the pathway, a soluble UDP-glucose glucosyl-transferase, to the microsomal system were unsuccesful.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(19)85850-7