Phenylacetate 4hydroxylase

Diethyldithiocarbamate and a,a-dipyridyl are inhibitors [A203].

This activity has been demonstrated in bacteria [B950], Aspergillus niger [A3787], A. fumigatus [C484], Brevibacterium linens [D623] and Trichosporon cutaneum [E332].

Phenylacetate 4-hydroxylase

Phenylacetate 0 ^-hydroxyphenylacetate

This activity has been demonstrated in bacteria [B950], Brevibacterium linens [D623], Trichosporon cutaneum [E332] and Aspergillus niger [A329].

Mandelate 4-monooxygenase (E.C. 1.14.16.6)

l-Mandelate 0 ^-hydroxymandelate

Pseudomonas convexa enzyme, molecular weight 91 000 and optimum pH 5.4, is inducible. It requires a tetrahydropteridine, NADPH, Fe2 + and oxygen, and is highly specific for mandelate. The activity is inhibited by thiol-binding reagents [A2662].

o -Hydroxyphenylacetate 5-hydroxylase o-Hydroxyphenylacetate 0 homogentisate

Rhodococcus erythropolis enzyme, molecular weight 45 000, contains FAD and requires NADH for activity [J23].

m -Hydroxyphenylacetate 4-hydroxylase

m-Hydroxyphenylacetate 0 3,4-dihydroxyphenylacetate

Klebsiella pneumoniae requires NADH or NADPH [G214]. The reaction has also been observed in Escherichia [B517], Trichosporon [E332], and possibly other microorganisms.

3-Hydroxyphenylacetate 6-hydroxylase

m-Hydroxyphenylacetate 0 homogentisate

Flavobacterium enzyme, which is mainly dimeric with one FAD/subunit and optimum pH 8.3, requires NAD(P)H as co-substrate; the amino acid composition and N-terminal sequence have been determined. It is stable between pH 5 and 9. Inactivation by thiol-binding reagents is reversed by dithiothreitol. Other substrates (less good) are 3,4-dihydroxyphenylacetate and p-hydroxyphenylacetate, with hydroxylation exclusively at position 6 [K779].

Rhodococcus erythropolis enzyme, molecular weight 45 000, contains FAD and requires NADH for activity [J23]. Flavobacterium enzyme, optimum pH 8.3, requires NAD(P)H. Poorer substrates include 3,4-dihydroxyphenylacetate and p -hydroxyphenylacetate, whereas homogentisate is not a substrate [G404].

p -Hydroxyphenylacetate 1-hydroxylase

^-Hydroxyphenylacetate 0 homogentisate

In this reaction the side chain migrates during the hydroxylation ('NIH shift').

Bacterium enzyme, optimum pH about 7.5, is stoichiometric for oxygen and NAD(P)H, and is slightly stimulated by Mg2 + ; its stability range is pH 6-9. Other substrates include p -hydroxy-phenylpyruvate, 3,4-dihydroxyphenylacetate, p -hydroxyphenylpropionate and (poor) p -hydroxybenzoate. It is inhibited by iodoacetate, iodoacetanilide, p -chloromercuribenzoate, iodosobenzoate, N-ethylmaleimide, Hg2+ and EDTA [A489].

Pseudomonas acidovorans enzyme requires FAD, Mg2+ and NAD(P)H, and is inhibited by KCl. It is unstable when purified. Substrate substituted with deuterium in the ortho position shows 50 per cent label retention, consistent with no NIH shift. Other substrates include dopac, homovanillate, p -hydroxyphenoxyacetate,

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