4-hydroxyphenylacetaldehyde oxime monooxygenase (, CYP71E1) is an enzyme that catalyzes a sequence of three chemical reactions that are part of the biosynthesis of the cyanogenic glycoside dhurrin in sorghum.
An earlier enzyme, tyrosine N-monooxygenase, in the pathway to dhurrin converts L-tyrosine to (E)-(4-hydroxyphenyl)acetaldehyde oxime. The first reaction catalysed by 4-hydroxyphenylacetaldehyde oxime monooxygenase isomerises this compound to the (Z) oxime:
The enzyme then catalyses the loss of water from the intermediate (Z)-oxime, giving 4-hydroxyphenylacetonitrile:
Finally, the cytochrome P450 component of the enzyme uses nicotinamide adenine dinucleotide phosphate (NADPH) and molecular oxygen to convert 4-hydroxyphenylacetonitrile to (S)-4-hydroxymandelonitrile.
(S)-4-hydroxymandelonitrile is converted to dhurrin by the enzyme cyanohydrin beta-glucosyltransferase.
The systematic name of this enzyme class is (Z)-4-hydroxyphenylacetaldehyde oxime,NADPH:oxygen oxidoreductase. Other names in common use include 4-hydroxybenzeneacetaldehyde oxime monooxygenase, cytochrome P450II-dependent monooxygenase, NADPH-cytochrome P450 reductase (CYP71E1), CYP71E1, and 4-hydroxyphenylacetaldehyde oxime,NADPH:oxygen oxidoreductase.