The biosynthesis of cyanogenic glucosides in higher plants. The (E)- and (Z)-isomers of p-hydroxyphenylacetaldehyde oxime as intermediates in the biosynthesis of dhurrin in Sorghum bicolor (L.) Moench.
The biosynthesis of the tyrosine-derived cyanogenic glucoside dhurrin has been studied with a microsomal preparation obtained from etiolated seedlings of sorghum. The biosynthetic pathway involves tyrosine, N-hydroxytyrosine, and p-hydroxyphenylacetaldehyde oxime as early intermediates (Møller, B. L. and Conn, E. E. (1980) J. Biol. Chem. 254, 8575-8583). The use of deuterium-labeled tyrosine and mass spectrometric analyses demonstrate that the alpha-hydrogen atom of tyrosine is retained in the conversion of tyrosine to p-hydroxyphenylacetaldehyde oxime. This excludes p-hydroxyphenylpyruvic acid oxime as intermediate in the pathway. A high pressure liquid chromatography method was developed to separate the (E)- and (Z)-isomers of p-hydroxyphenylacetaldehyde oxime. The microsomal enzyme system was found to produce initially the (E)-isomer of p-hydroxyphenylacetaldehyde oxime. An isomerase then converts the (E)-isomer to the (Z)-isomer, which is the isomer preferentially utilized by the microsomal enzyme system in the subsequent biosynthetic reactions. The (E)-isomer produced in situ is more efficiently converted to the (Z)-isomer than exogenously added (E)-isomer and may thus be metabolically channeled.
Halkier
B A
BA
Department of Plant Physiology, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
Olsen
C E
CE
Møller
B L
BL
D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium; D005960:Glucosides / Q000096:biosynthesis*; D006027:Glycosides; D007536:Isomerism; D013058:Mass Spectrometry; D008861:Microsomes / Q000378:metabolism; D009570:Nitriles / Q000378:metabolism*; D010091:Oximes / Q000302:isolation & purification / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D014443:Tyrosine / Q000378:metabolism
D002250:Carbon Radioisotopes; D005960:Glucosides; D006027:Glycosides; D009570:Nitriles; D010091:Oximes; C020363:4-hydroxyphenylacetaldoxime; D014443:Tyrosine; D003903:Deuterium; C011220:dhurrin