a. Polynuclear hydrocarbons
Rat liver enzyme oxidizes 7-methyl- and 7,12-dimethylbenzanthracene, incorporating oxygen from molecular oxygen, but not from water [A339].
A Pseudomonas putida enzyme, which acts on 4-hydroxy-3-methylbenzoate is a 2-protein system, molecular weight 115 000, that appears to be composed of a flavin-containing hydroxylase and an electron-transfer system that uses NADH. It is claimed to be an unusual type of mixed-function oxidase [F223]. The electron transfer system appears to be a flavocytochrome c [A3870].
p-Cresol is converted into p -hydroxybenzyl alcohol by Pseudomonas 4-cresol dehydrogenase (hydroxylating) (E.C. 22.214.171.124), a dimer, molecular weight 115000. One component is a c-type cytochrome and the other a flavoprotein [A3276]; the oxygen is incorporated from water [A3829, K410]. Studies on p-cresol oxidation with 3 Pseudomonas strains including P. putida found that each has a different molecular weight and Km. The enzyme is anaerobic, with 8a-(O-tyrosyl)FAD as cofactor [B853, K841]. It further oxidizes the substrate to the corresponding aldehyde [A3829].
Pseudomonas p -cresol methylhydroxylase is a cytochrome c flavoprotein that catalyzes the incorporation of oxygen from water, and oxidizes the product further to the aldehyde [K203]. The enzyme is a tetramer with two pairs of identical polypeptide chains, one with molecular weight 119 000, and the other a cytochrome, molecular weight 9300; each of the latter binds a flavin molecule. In the wild-type enzyme this is covalently bound, but in enzyme expressed in E. coli it is not covalently bound [K289]. Growth on p -cresol induces the p -cresol oxidizing enzyme, which is a dimer, molecular weight 100 000, composed of a flavoprotein and cytochrome c, with different molecular weights and Km (not quoted) for the enzyme from three different strains [A3870, B853]. p -Cresol and p -ethylphenol are oxidized adjacent to the aromatic nucleus. A ping-pong mechanism has been suggested for the oxidation [E361].
3,5-Xylenol is oxidized in Pseudomonas putida by an enzyme that does not oxidize p -cresol. It requires NADH, and is inhibited by cyanide but not by carbon monoxide [A3870].
Penicillium simplicissimum vanillyl alcohol oxidase (E.C. 126.96.36.199) is a flavoprotein that acts on p -cresol [G662]; it also forms p -hydroxbenzaldehyde very slowly [J680].
P. patulum enzyme is microsomal, optimum pH 7.5, and requires molecular oxygen and NADPH for oxidation of p -cresol. Carbon monoxide and cytochrome c are inhibitory [A1468].
Achromobacter enzyme, molecular weight 130000, is composed of subunits, molecular weights 54 000 and 12 500. The substrate is p -cresol [F868].
c. Toluenes and xylenes
Pseudomonas aeruginosa enzyme is composed of three proteins, and requires FAD and NADH [A1009].
E. coli xylene monooxygenase oxidizes toluene and pseudocumene to the corresponding alcohols and aldehydes [K491].
Azoarcus enzyme, which is membrane-bound, requires quinone as an electron acceptor; the product is pure (S)-1-phenylethanol. Not all analogues are substrates, but propylbenzene and p -ethylfluorobenzene are hydroxylated [K241].
Byssochlamys fulva vanillyl alcohol oxidase is a homodimer, monomeric molecular weight 58 000, which oxidizes p -hydroxyphenylethane and p -hydroxyphenylpropane to the corresponding (S)-1-(p -hydroxyphenyl)alcohols [K164].
E.coli enzyme forms mainly the (R )-isomer [G740]
Mortierella isabellina enzyme forms both (R)- and (S)-phenylethanols, and the identity of the para substituent determines which predominates. In no case was one isomer found to be the exclusive product. With bromo and nitro substitution the enantiomeric enrichment was only slight, whereas with methoxy and chloro (S) predominates (between 20 per cent and 40 per cent enantiomeric excess), but with cyano, methyl, ethyl and fluoro (R) predominates [D969].
A Penicillium simplicissimum vanillyl alcohol oxidase acts on 4-allyl- and 4-alkylphenols (1-3 C chain). Further oxidation forms the corresponding acetophenone and propiophenone. p -Propylphenol also forms a small amount of p -coumaryl alcohol, and ethylphenol and propylphenol form vinylphenol and propenylphenol respectively. A quinone methide intermediate is probable for the formation of (R )-benzylic alcohols, which are formed in about 94 per cent enantiomeric purity. The hydroxyl group comes from water [J16, J664, J680].
The (S)-isomer is formed by Pseudomonas from ethylbenzene [J219]. P. fluorescens eugenol dehydrogenase forms (S)-1-(p -hydroxyphenyl)ethanol and (S)-1-(p -hydroxyphenyl)propanol from the corresponding 4-alkylphenols [K177].
Pseudomonas putida 4-ethylphenol methylenehydroxylase is a flavocytochrome c composed of two pairs of subunits, molecular weight about 120000. One subunit, molecular weight 50 000 is a flavoprotein and the other, molecular weight 10 000 is a cytochrome c. The mechanism involves dehydrogenation followed by hydration to form 1-(p -hydroxyphenyl)ethanol. It acts on a range of 4-alkylphenols with up to nine carbon atoms in the side chain and on 5-indanol (a cyclic analogue of 4-ethylphenol). p -Cresol and 2,4-xylenol are substrates; and 1-(p -hydroxyphenyl)ethanol is further oxidized to p -hydroxyacetophenone. It is considered that the reaction proceeds via a quinone methide [F381]. In another study the enzyme was called 4-ethylphenol methylenehydroxylase [E396].
This type of reaction has also been observed in man [D482], rat [D365], rabbit [A287], chinook salmon [E710], Desulfobacula toluolica [J847], Nocardia tartaricans [B144] and in Nitrosomonas [H219]; in N. europaea ammonia monooxygenase catalyzes the reaction [H631]; in many studies, particularly the early ones the chirality of the product was not established.
Penicillium simplicissimum vanillyl alcohol oxidase hydroxylates eugenol and chavicol to the corresponding cinnamyl alcohols [H389]. The enzyme also carries out a range of other activities, such as oxidizing secondary vanillyl alcohols, including phenylethanolamines, to the corresponding ketones [J16].
Byssochlamys fulva enzyme is a homodimer, monomeric molecular weight 58 000, which additionally oxidizes vanillyl alcohol to vanillin, and (p-hydroxyphenyl)alkanes to (S)-1-(p -hydroxyphenyl)alcohols [K164].
Pseudomonas fluorescens eugenol dehydrogenase, a dimer, monomeric molecular weights 10 000 and 58 000, is a flavoprotein that requires an oxidizing agent, such as ferricyanide. It forms coniferyl alcohol from eugenol, as well as oxidizing p -hydroxybenzyl alcohols [J890].
Solanum khasianum enzyme, which hydroxylates the terminal carbon of acetovanillone, requires oxygen and NADPH. Its inhibition properties are like those of P450 [H906]. A similar reaction probably occurs in Pseudomonas with acetophenone [J219].
In rat a similar reaction occurs with paeonol [E849].
Extensive studies with cannabinoids have demonstrated that hydroxylations occur at various positions in the molecule; however, little appears to have been done at an enzyme level. The literature on this subject is extensive, and the references given (for A^tetrahydrocannabinol) are illustrative.
Cannabinoid 1 "-hydroxylation
This reaction has been detected in guinea pig and Thamnidium [B458, B742].
This reaction has been detected in man, guinea pig, Fusarium, Gibberella and Thamnidium [B458, B742, C2, F819].
This reaction has been detected in mouse, rat, guinea pig, monkey, Chaetomium, Fusarium, Gibberella and Thamnidium [A3628, B458, B742, E598, F599, F819, H418].
This reaction has been detected in guinea pig, rat, rabbit, Fusarium, Gibberella, Syncephalastrum and Thamnidium [A2595, B458, B742, E7, F7]
This reaction has been detected in mouse, rabbit and guinea pig [A3449, F7].
This reaction has been detected in rat, rabbit, monkey, man, mouse and Chaetomium [A108, A116, A438, A680, A879, A3628].
Claviceps microsomal enzyme, a P450 that requires NADPH, hydroxylates agroclavine to elymoclavine [B809].
3.2 Alkyl oxidation to ketone
Phenylacetyl CoA: acceptor oxidoreductase
Phenylacetyl CoA + 2 quinone + 2 H2O 0 phenylglyoxylate + 2 quinol + CoASH
Thauera aromatica enzyme is a membrane-bound trimer, subunit molecular weights 93 000, 27 000
and 26 000, with an assumed native molecular weight of 280 000. Analyses indicate that this contains 0.66 Mo, 30 Fe and 25 acid-labile S. The reaction is anaerobic, with duroquinone, menadione or (best) dichlorophenolindophenol as electron acceptors. Phenylglyoxylyl CoA is an intermediate, but mandelyl CoA is not [K173].
3.3 Oxidations and reductions of alcohols, aldehydes and ketones
Alcohol dehydrogenases (aryl-alcohol dehydrogenase; E.C. 188.8.131.52, aryl-alcohol dehydrogenase (NADPH); E.C. 184.108.40.206)
Human brain enzyme is composed of at least five isozymes, pI 5.3, 6.0, 6.3, 7.0 and 7.9. They all act on p -nitrobenzaldehyde and indole-3-acetaldehyde, but are distinguished by their relative activities towards menadione, daunorubicin, p -hydroxyphenylacetaldehyde and p -hydroxymandelaldehyde as potential substrates. All require NADPH; one that can also utilize NADH appears to be succinic semialdehyde reductase (E.C. 220.127.116.11/ E.C. 18.104.22.168). The pI 7.9 enzyme is strongly inhibited by quercetin and quercitrin [B569].
Human brain aflatoxin B1 aldehyde reductase is identical with succinic semialdehyde reductase, which also reduces phenanthrene-9,10-quinone, phenylglyoxal and p -nitrobenzaldehyde [K273].
Horse liver enzyme oxidizes benzyl alcohol reversibly; the enzyme has two active sites [A2174].
A Glycine max (soyabean) cinnamyl alcohol dehydrogenase isozyme (E.C22.214.171.124), molecular weight 43 000 and optimum pH 9.2, oxidizes coniferyl alcohol. A second isozyme in addition reversibly oxidizes several substituted cinnamyl alcohols with optimum pH 8.8, and optimum pH 6.6 for reduction [A2325].
Rye aromatic alcohol dehydrogenase is composed of 3 NADP-dependent isozymes, one
NAD-dependent isozyme and one without nucleotide specifity [D45].
Acinetobacter calcoaceticus benzyl alcohol dehydrogenase is a monomer, molecular weight 38 923 with 370 amino acid residues, based on nucleotide sequencing. It requires NADH and zinc; it is a member of a family of zinc-dependent long-chain alcohol dehydrogenases (E.C. 126.96.36.199) [J621]. Other substrates include coniferyl alcohol, cinnamyl alcohol and other (unspecified) aromatic alcohols, but few aliphatic alcohols are substrates [E473]. Another study claims that the enzyme is a tetramer with a monomeric molecular weight consistent with the above value. The optimum pH for oxidation is 9.2, and for reduction 8.9 [E596].
Azoarcus 1-phenylethanol dehydrogenase, which is inducible, only acts on the (S)-isomer; it requires NAD + [K241].
Geotrichum candidum converts (S)-arylethanols into (R)-arylethanols via acetophenones; (R)-arylethanols are not substrates. A range of phenylethanols substituted on the aromatic nucleus with chloro, methyl and methoxy groups (but not in the ortho position) are also substrates [H749].
A methanol dehydrogenase (E.C. 188.8.131.52) in Methylomonas methanica, molecular weight 60 000, oxidizes 2-phenoxyethanol and a range of aliphatic alcohols at similar rates, but does not act on benzyl alcohol or secondary alcohols. It requires NH4+ , with optimum pH 9.5 [A27l2].
Mycobacterium tuberculosis enzyme has an optimum of 6.5-8, depending on the nature of the buffer and other parameters. It oxidizes benzyl alcohols as well as reducing benzaldehyde. It is inhibited by p -chloromercuribenzoate, benzoate and o-phenanthroline [A150].
Penicillium urticae 3-hydroxybenzyl-alcohol dehydrogenase (E.C. 184.108.40.206), molecular weight 120 000 and optimum pH 7.6, requires NADP. It is a key enzyme in the formation of patulin from 6-methylsalicylate [K946].
Penicillium simplicissimum vanillyl alcohol oxidase (E.C. 220.127.116.11) is an octomer, monomeric molecular weight 65 000. It is a flavoprotein (1 mol/mol of monomer), with covalently bound 8a-(N3-histidyl)FAD. It is highly specific for p -hydroxybenzyl alcohols [G662]. It forms the corresponding acetophenone and propiophenone from p -ethylphenol and p -propylphenol; there is good evidence that the corresponding alcohols are intermediates [J664, J680].
Phanerochaete chrysosporium enzyme, molecular weight 78 000, has a FAD prosthetic group. It is specific for benzyl alcohols [H613].
Pleurotus eryngii alcohol oxidase (E.C. 18.104.22.168), molecular weight 72600 and pI 3.9, contains 15 per cent carbohydrate. It oxidizes a series of benzyl and cinnamyl alcohols [G668]. P. pulmonarius enzyme which contains 14 per cent carbohydrate, molecular weight 70 500 and pI 3.95, has been crystallized. DNA studies indicate that it is composed of 593 amino acid residues, including a signal peptide of 27 amino acid residues [K373].
Pleurotus ostreatus veratryl alcohol oxidase is a glycoprotein containing FAD, optimum pH 6.5 (broad), which forms veratraldehyde, with oxygen forming peroxide. A range of benzyl alcohols and cinnamyl alcohols are oxidized [F867].
Polystictus versicolor aryl alcohol oxidase is found in the media surrounding the mycelia. It acts on several benzyl alcohols and 2-hydroxymethylnaphthalene, but other alcohols are only marginally active [K878].
Pseudomonas fluorescens enzyme, a dimer, monomeric molecular weights 10 000 and 58 000, is a flavoprotein requiring an oxidizing agent, such as ferricyanide. It oxidizes p -hydroxybenzyl alcohols as well as forming coniferol alcohol from eugenol [J890].
Pseudomonas putida grown on 3,5-xylenol contains two NAD + -dependent alcohol dehydrogenases, molecular weights 122000 and 145000. When grown on p-cresol a single NAD +-dependent alcohol dehydrogenase develops, molecular weight 75 000. They all have an optimum pH of 9.5 or higher, and oxidize a range of substituted benzyl alcohols with minor differences in specificity. The xylenol-induced enzymes that oxidize benzyl alcohol, m- and p -hydroxybenzyl alcohols undergo spontaneous inactivation, and are protected by dithiothreitol. Inactivation by p -chloromercuribenzoate is partly prevented by substrate [A1366, A3837].
Pseudomonas putida 4-ethylphenol methylenehydroxylase (see Ethylbenzene dehydrogenases, above) oxidizes 1-(p -hydroxy-phenyl)ethanol to p -hydroxyacetophenone [F381].
Pseudomonas syringae d-phenylserine dehydrogenase, molecular weight 31 000 and optimum pH 10.4, requires NADP+ [H91].
Rhodopseudomonas acidophila p -hydroxy-benzyl alcohol dehydrogenase (E.C. 22.214.171.124), molecular weight 27000 and pI 7.4, has an optimum pH 6.5 for oxidation and pH 9 (broad) for the reverse reaction. Substrates include cinnamyl alcohol, phenylethanol and a series of benzyl alcohol analogues substituted in the m- and p -positions, but not o-analogues [Dl97].
Thauera benzyl alcohol dehydrogenase, which is a homotetramer, molecular weight 160 000, requires NAD+ [H610].
A benzyl alcohol dehydrogenase has been detected in a Bacterium [A730].
Aromatic aldehyde and ketone reductases (aryl alcohol oxidase, E.C. 126.96.36.199; c.f. aryl-alcohol dehydrogenase (NADP + ); E.C. 188.8.131.52)
R.CO.R -> R.CHOH.R, where R is H or an alkyl group and R? an aryl or an aralkyl group.
Four or possibly 5 isozymes of aldehyde reductase in human brain reduce indole-3-acetaldehyde and p -nitrobenzaldehyde, with pI 5.3 (this isozyme appears to be E.C. 184.108.40.206), 6.0, 6.3, and the fourth fraction shows two values at 7.0 (minor) and 7.9. They require NADPH, although one isozyme can utilize NADH. Menadione, daunorubicin, p- hydroxyphenylacetaldehyde and p -hydroxymandelaldehyde are substrates for at least 2 of the isozymes. [B569].
Human erythrocyte 4-nitroacetophenone reductase, optimum pH about 7, is not cytochrome c. It requires NADPH, but not NADH. It is unstable at 50°, and is moderately unstable at 4° and is inhibited by p -nitrobenzaldehyde, p -chloromercuribenzoate and N-ethylmaleimide, and slightly by methanol. It is claimed to differ from other side chain keto reductases. A similar enzyme is found in rat [A15].
Beef enzyme is widely distributed throughout the brain [A1908]. It requires NADH; NADPH is a poor co-substrate. The optimum pH for reduction is 6.8, and 10 for the reverse reaction. Some aliphatics as well as p-nitrobenzaldehyde are substrates [A614].
Pig brain contains two isozymes, one low- and the other high-affinity. Both reduce 3,4-dihydroxy- and 4-hydroxy-3-methoxyphenylacetaldehydes as well as l -p -hydroxyphenylglycolaldehyde and d-3,4-dihydroxyphenylglycolaldehyde; the high affinity isozyme also reduces 5-hydroxyindole-3-acetaldehyde [A1287]. Another study found the molecular weight of the cytosolic enzyme to be 29000 and pI 5.8. It utilizes NADPH in the reduction of benzaldehydes, p -hydroxy-mandelaldehyde, indole-3-acetaldehyde and some aliphatic aldehydes (especially lactaldehyde and glyceraldehyde; acetaldehyde is very poor), but it is ineffective in reducing ketones [Al679].
Monkey (apparently rhesus) brain enzymes have a similar specificity to that of pig brain enzyme. Both isozymes require NADPH; one is low affinity and high activity and the other high affinity and low activity [A1908].
Rat liver aldehyde reductase isozymes, pI 6.5 and 6.9, reduce 3,5-dihydroxyphenylacetaldehyde and p -nitrobenzaldehyde [B659]. An enzyme tentatively identified as E.C. 220.127.116.11 has an optimum pH of 6 /8 for the forward reaction, whereas the optimum for the reverse reaction (on daunorubicinol) is above pH 10. Both aliphatic and aromatic aldehydes are reduced, the best being 4-carboxybenzaldehyde; adriamycin is reduced, but only poorly. Barbital, warfarin and phenobarbital are inhibitors, but is activated by NaCl, with peak activity enhanced by 50 per cent above the base-line activity at ionic strength 0.4. With 50 mM sodium sulphate there is 40 per cent activation, which declines to zero at ionic strength 0.3 /0.4, with inhibition at higher concentrations [A2007]. A rat liver aldehyde reductase, optimum pH 6.5, reduces many benzaldehydes, as well as quinones and phenylglyoxal. It differs in specificity from other aldehyde reductases in that it reduces o -quinones; it is the only one found in this study that reduces aflatoxin B1-dialdehyde, a very poor substrate [H759].
Rat liver cytosol contains a highly specific 2-carboxybenzaldehyde reductase, molecular weight 64000; the 3- and 4-carboxy analogues are not substrates. It requires NAD(P)H and a thiol for activity [G239].
Rat aflatoxin B1 aldehyde reductase 2 is found as multiple forms, with molecular weights in the range 36 800 and 38 000. They also act on other aldehydes and quinones [K546].
A rabbit liver cytosolic enzyme, molecular weight 33 000 and optimum pH 6.2, reduces the oxo group of loxoprofen and requires NADPH. It also reduces benzaldehydes, acetophenones and various other oxo-compounds. A similar activity that reduces loxoprofen is found in guinea pig [D125]. Another study with rabbit liver cytosol found four isozymes, designated F1, F2, F3 and F4. F2 is an aldehyde reductase, whereas the others are aromatic aldehyde/ketone reductases. F1 and F3 are monomeric with molecular weights 38 000 and 29 000 respectively. F4 appears to be trimeric, molecular weight 78 000, and monomeric molecular weights 24 000 and 26 000. Substrates include 3- and 4-benzoylpyridines and p-nitroacetophenone [B431]. Flavonoids are inhibitory [K560]. A further publication reports molecular weights that differ appreciably from these values; it also describes a benzaldehyde-reducing enzyme that does not reduce acetophenones, whereas two acetophenone-reducing enzymes also reduce some benzaldehydes [B386]. Seven isozymes were detected in one study. Two are aldehyde reductases, the major having pI 6.0 /6.3 and the minor 7.8. A major enzyme, pI 4.9, is active towards p-nitrobenzaldehyde and p -nitroacetophenone, but not naloxone or naltrexone. Four others, including one major enzyme, which reduce naloxone and naltrexone as well as other carbonyl compounds, were named dihydromorphinone reductases, pIs 5.4 /5.5, 6.5, 6.6 and 6.9 7.2 [A3950]. Rabbit and chicken dihydromorphinone reductases require NADPH, and are found mainly in liver cytosol, although some activity is present in kidney and lung [A2290].
An enzyme in rabbit, rat and guinea pig liver that reduces substituted benzoylpyridines is found in both microsomes and cytosol (the latter not in rat), and requires NADPH. Cytosolic enzyme is inhibited by heavy metals, o -phenanthroline and azide among other compounds, whereas the microsomal enzyme is inhibited by Hg2 + , p -chloromercuribenzoate and N-ethylmaleimide [A2834].
Sheep heart enzyme reduces a range of phenylglycolaldehydes and oxidizes p- hydroxybenzaldehyde, and requires NADP as co-substrate [A57].
Cucumis sativus (cucumber) cytoplasmic indole-3-acetaldehyde reductase (E.C. 18.104.22.168) is highly specific and requires NADPH [F462]. Another study identified 3 indole-3-acetaldehyde reductase isozymes. Two, molecular weights 17000 and 52000 and optimum pH 5.2, require NADPH. A NADH-specific enzyme (E.C. 22.214.171.124) has a molecular weight of 332000 and optimum pH 7.0. They all reduce phenylacetaldehyde and (poorly) trans- cinnamaldehyde. Some aliphatics are poor substrates, but benzaldehydes are not reduced [A2432].
A mung bean monomeric enzyme, molecular weight 36 000 and optimum pH 6.2 7.5, reduces eutypine irreversibly, and a series of benzaldehydes and cinnamaldehyde with NADPH as cofactor; it appears that no tests were made on the reversibility with these other substrates [J910].
Populus euramericana stem cinnamyl alcohol dehydrogenase, molecular weight 36 000 and pI 5.6, requires NADPH for the reduction of coniferaldehyde, p-coumaraldehyde and sinapaldehyde, and is inhibited by 1,l0-phenanthroline and sulphydryl-binding compounds [D54].
Both spruce and Glycine max contain cinnamyl alcohol: NADP+ dehydrogenases (E.C. 126.96.36.199) that reduce coniferaldehyde, p -coumaraldehyde and sinapaldehyde. Both are dimers, monomeric molecular weight about 35000 [B922]. Another study on the Glycine enzyme found a molecular weight of 40 000 for a zinc-containing isozyme that reduces coniferaldehyde. It requires NADPH, and is inhibited by thiol-binding reagents [B95].
Swede enzyme, which is composed of three isozymes, is part of the system for forming coniferyl alcohol from ferulate. It requires NADPH (NADH is inactive) for the reduction of coniferaldehyde, and is reversible [A216]. Forsythia enzyme is very similar [A848].
Candida guilliermondii contains a phenylacetaldehyde reductase that requires NAD(P)H [A2483].
Corynebacterium phenylacetaldehyde reductase requires NADH. It also reduces nuclear substituted phenylacetaldehydes, phenacyl chloride, acetophenone, propiophenone and 4-phenylbutan-2-one stereoselectively to the (S)-alcohol (phenacyl chloride yields the (R)-isomer with the same spatial geometry). In the reverse reaction the (S)-alcohols are substrates [J893].
Geotrichum candidum reduces acetophenones [H749].
Lactobacillus kefir acetophenone reductase, optimum pH 7.0, which is protected by Mg2 + , requires NADPH, but NADH is inactive. The optimum pH for reduction is 7.0, and for oxidation 8.0. Propiophenone, a range of acetophenones, and some (but not all) other analogues tested, as well as benzaldehyde, are substrates. The product from acetophenone is (R )-(+)-1-phenylethanol, which is a substrate for the reverse reaction, although (S)-1-phenylethanol is not [Gl48].
Phycomyces blakesleeanus indole-3-acetaldehyde reductase is a tetramer, monomeric molecular weight 38 000, pI 5.4 and optimum pH 6-8. It requires NAD(P)H as cofactor [F846].
A Pseudomonas guaiacylglycerol b-guaiacyl ether dehydrogenase reduces the a-oxo analogue of this compound [G357].
Cucumber enzyme is inhibited by the reaction product, and this inhibition is reversed by oxygen but not by the substrate. Several auxins are inhibitory [A835, A957]; this undoubtedly prevents over-production of IAA.
Phaseolus vulgaris, molecular weight 56 000, requires oxygen, and forms peroxide as a second product [H554].
Phycomyces blakesleeanus enzyme, molecular weight 56 000 and optimum pH 6-8, forms indole-3-acetaldehyde and possibly peroxide. It is activated by FAD and inhibited by Hg2+ , iodoacetate, and by 4 mM indole-3-acetaldehyde [E443].
Mandelate dehydrogenases and oxidases
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