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Rhodotorula graminis l-( )-mandelate dehydrogenase is a tetramer, monomeric molecular weight 59 100, that contains one mol each of haem and FMN per subunit. The optimum pH is 7.9, and pI 4.4. It acts on mandelate and a series of nuclear-substituted analogues [H90] and is stereospecific [G904]. Both d- and l-dehydrogenases are inducible. l-Dehydrogenase, optimum pH 7.0, requires dichlorophenolindophenol as reductant, and may be membrane-bound; activity is enhanced by phenazine methosulphate. d-Dehydrogenase, optimum pH 9.0, is not membrane-bound, and requires NAD+ [D475].

Acinetobacter calcoaceticus enzymes, specific for each stereoisomer are found in cytoplasmic membranes. After solubilization, the d-dehydrogenase has a molecular weight of 59 700, optimum pH 8.0 and pI 5.5 [D870] and are very similar to the corresponding d- and l-lactate dehydrogenases (E.C. 1.1.2.4 and 1.1.2.3 respectively) [D674]. A novel enzyme found in a mutant strain but not in the wild-type organism, acts solely on the d-isomer. It is membrane-bound, and its pH and temperature dependence are similar to those of the l-dehydrogenase (the activity found in most strains). Inhibitors include l-mandelate [A1649, C801].

Aspergillus niger d-mandelate oxidase (not a dehydrogenase), optimum pH 7.6, is particulate and very unstable. It is specific for the d-isomer of several mandelates. Neither NAD nor NADP+ are involved, and metal ions are not activators. It appears to require cytochrome c and molecular oxygen, which cannot be replaced by other oxidizing agents, and peroxide is not formed as a second product. Heavy metal ions are inhibitors [A1204].

Pseudomonas putida (S)-mandelate dehydrogenase oxidizes mandelate and indole-3-glycollate, and acts very slowly on plenyllactate, indole-3-lactate and some aliphatic analogues [K95]. It is membrane-bound, with a binding segment of about 39 residues [K230].

Rhizobium leguminosarum enzyme is induced by 4-hydroxymandelate [F224].

A Bacterium (unidentified) enzyme, optimum pH 9.5, oxidizes d-VMA to the corresponding benzoylformate, but d-mandelate is not a substrate [J256]. Another study has identified a l-dehydrogenase in a Bacterium [A730].

Indole-3-acetaldehyde reductase (E C. 1.1.1.190 and 1.1.1.191)

Indole-3-acetaldehyde 0 tryptophol

Human brain enzyme acts on indole-3-acetaldehyde [B569]. Rat liver enzyme [A2007] and pig brain enzyme [A1679] also reduce other aldehydes (see above).

Brassica campestris (Chinese cabbage), molecular weight 32000 and optimum pH 6-7 requires NADPH. Other substrates are benzaldehyde and phenylacetaldehyde, but not 3-formylindole. It has also been found in B. napus, B. oleracea, Arabidopsis thahana and Sinapis alba [F931].

Cucumis sativa (cucumber) enzyme, which requires NADPH, is cytoplasmic and is specific for indole-3-acetaldehyde [F462].

Mung bean enzyme, a dimer, monomeric molecular weight 39 000, requires NADPH. It also reduces benzaldehyde and phenylacetaldehyde [J207].

Phycomyces blakesleeanus enzyme, molecular weight 38 000, pI 5.4 and optimum pH 6-8 requires NAD(P)H [F846].

This reduction has also been detected in Orobanche gracilis, O. lutea, O. ramosa [C181], Zygosaccharomyces [A923] and pea [A755].

Benzoylformate reductase

Benzoylformate 0 mandelate

This activity has been found in rats [J287], with a preponderance (10:1) of the (R)-isomer formed [F496].

Pseudomonas polycolor and Micrococcus freundii catalyse this reaction; this enables racemic mandelate to be converted into the (R )-isomer, because these organisms contain an enzyme that converts (S)-mandelate into benzoylformate, but is inactive towards (R )-mandelate [H668].

S. faecalis enzyme is dimeric, molecular weight 72000, pI 4.9 and optimum pH 4.5, also reduces phenylpyruvate and some aliphatics, but not p -hydroxyphenylpyruvate or p -hydroxybenzoylformate. The optimum pH for the reverse reaction is 9.2 [E271].

Hydroxyphenylpyruvate reductase (E C. 1.1.1.237)

Coleus blumei enzyme, which requires NADH reduces p -hydroxyphenylpyruvate and 3,4-dihydroxyphenylpyruvate to the corresponding lactates [E660].

Aromatic a-ketoacid reductase ((R)-aromatic lactate dehydrogenase; 1.1.1.222, diiodophenylpyruvate reductase; E.C. 1.1.1.96)

1. Reduction

Dog heart enzyme is a cytosolic dimer, monomeric molecular weight 40000, pI 5.4, which requires NADH. Activity is also found in brain, kidney and liver, and is considered to be associated with an isozyme of malate dehydrogenase. The best substrate is 3,5-diiodophenylpyruvate, with good activity towards phenylpyruvate and indole-3-pyruvate [A2917].

In vivo studies have demonstrated this activity in rat [A2961, A3327]; reduction is catalyzed by lactate dehydrogenase (E.C. 1.1.2.3) and aromatic alpha-keto acid reductase [A3327]. Highest activity is found in heart, and (in reducing order) in kidney, muscle and liver. 3,4-Dihydroxyphe-nylpyruvate is 10 times as active as 3-methoxy-4-hydroxyphenylpyruvate. Oxamate (a lactate dehydrogenase inhibitor) does not inhibit liver mitochondrial enzyme [A2983].

In a range of animals cytoplasmic malate dehydrogenase (E.C. 1.1.1.37) has been found to be identical with aromatic alpha-keto acid reductase (with p -hydroxyphenylpyruvate as substrate), with lactate dehydrogenase accounting for a minimal proportion of the total activity found in these species. The studies were carried out on flight muscle of Falco, Milvago, Herpetotheres, Phalcobanes, Spiziapteryx and Polyhierax, Palaemonedes (a marine invertebrate), and frog liver and muscle. The activity in Fundulus grandis (a marine fish) is identified as lactate dehydrogenase [E561].

Coleus blumei enzyme has an optimum pH between 6.5 and 7.0, requires NAD(P)H, and reduces the physiologically important pyruvates m- and p -hydroxy-, 3,4-dihydroxy- and 4-hydroxy-3-methoxyphenylpyruvates [E660, G289].

Candida guilliermondi enzyme requires NAD(P)H [A2483].

Candida maltosa enzyme is a tetramer, molecular weight 250 000 /280 000, monomeric molecular weight 68 000. It requires Mn2+ and NAD(P)H for reduction; the reaction is reversible, with optimum pH 6.5 for reduction, and 9.5 for oxidation. Substrates studied are phenylpyruvate, p -hydroxyphenylpyruvate, indole-3-pyruvate and the corresponding lactates [D975].

Lactobacillus casei d-hydroxyisocaproate dehydrogenase reduces phenylpyruvate to d-phenyllactate [E587].

2. Oxidation (indolelactate dehydrogenase; E.C. 1.1.1.110)

Formation of phenylpyruvate from phenyllactate has been recorded in rat, Candida, Lactobacillus, Neisseria, Pseudomonas and Rhodotorula

[B438, D975, E377, F92, G774, K95]. A similar reaction has been detected in rat for m-hydroxyphenyllactate and vanillactate [A2961]. In addition, p -hydroxyphenyllactate is oxidized by Neisseria gonorrhoeae [F92], and indole-3-lactate by Candida maltosa (see above) [D975].

Cinnamyl alcohol dehydrogenase (E.C. 1.1.1.195)

Aralia cordata enzyme is a heterodimer, molecular weight 72 000. The reaction is reversible, the reverse requiring NADPH. Substrates are coniferaldehyde, sinapaldehyde, coniferyl alcohol and sinapyl alcohol [G815].

Eucalyptus gunnii contains two isozymes; one is monomeric, molecular weight 38 000, and the other, molecular weight 83 000, is a heterodimer [G660].

Loblolly pine enzyme is a dimer, monomeric molecular weight 44 000. It reduces coniferaldehyde and sinapaldehyde [G484].

Nicotiana enzyme, which is composed of two isozymes, molecular weights 42 500 and 44 000, requires NADP [G458].

Spruce (Picea abies) enzyme is a dimer, molecular weight 42000. Substrates are coniferaldehyde, p-coumaraldehyde, coniferyl alcohol and p -coumaryl alcohol with NADP(H) as co-substrate [G781].

Etiolated wheat seedlings contain three isozymes; the molecular weights of two of these are 40 000 and 45 000. Substrates are coniferaldehyde, p-coumaraldehyde and sinapaldehyde [H510].

Among those species studied, the enzyme is not found in Pteridophyta or monocotyledonous angiosperms (except Zea). It is mostly found in gymnosperms and dicotyledonous angiosperms. It is usually a single enzyme, except in a range of Salix species (three to eight isozymes, usually four). It is not the same as alcohol dehydrogenase; it requires NADP, whereas alcohol dehydrogenase requires NAD [A1732].

Benzyl 2-methyl-hydroxybutyrate dehydrogenase

Benzyl 2-methyl-hydroxybutyrate dehydrogenase

Reduction of benzyl 3-oxo-2-methybutyrate to (2R,3S)- and (2S,3S)-benzyl 3-hydroxy-2-methylbutyrate in Candida albicans, Endomycopsis fibligera, Hansenula anomala, Lipomyces starkeyi, Pichia farinosa, P. membranaefaciens, Rhodotorula glutinis, Saccharomyces cerevisia and S. acidifaciens has been detected [K940].

Methyl 2-oxo-3-phenylbutyrate reduction

This reaction has been found in Candida albicans, Endomycopsis fibligera, Hansenula anomala, Kloeckera saturnus, Lipomyces starkeyi, Pichia farinosa, P. membranaefaciens, Rhodotorula glutinis, Saccharomyces cerevisiae, S. acidifaciens, S. delbruechii and S. fermentati. Different organisms form different ratios of stereoisomers [K883].

2-Hydroxy-6-oxo-6-phenylhexa-2,4-dienoate reductase (E.C. 1.3.1.40)

Pseudomonas cruciviae enzyme is composed of three isozymes. One, molecular weight 170000, requires NADPH, and also reduces the methyl ester of the above compound (which forms 2,6-dioxo-6-phenylhexanoate) [E156].

Indanol dehydrogenase

(S)-l-Indanol i 1-indanone

Human placenta oxidizes 1-indanol to 1-indanone, with NAD(P)+ as cofactor. Most of the activity is present in microsomes, with some in mitochondria but little in the cytoplasm [D415].

Japanese monkey liver cytosolic enzyme, molecular weight 36000 and pI 8.7, requires NAD(P) + for oxidation and NADPH for reduction; the amino acid composition has been determined. The specificity is broad for cyclic alcohols such as (S)-1-indanol, benzene-1,2-dihydrodiol and 1-hydroxytetralin, and for aldehydes and ketones in which the oxo-group is conjugated with the aromatic nucleus, such as benzaldehydes and acetophenones. The activity with (R )-1-indanol is much lower than with (S)-1-indanol [F241]. Four isozymes have been found, two major and two minor; classical indanol dehydrogenase is one of the major isozymes. Quantitative studies show that (S)-l-indanol and 1-acenaphthenol are the best substrates. One minor isozyme has a similar specificity, and differs mainly in that the pI is 7.9. The other major isozyme, molecular weight 38 000 and pI 6.2, shows a similar activity for each substrate studied. The product from benzene-1,2-dihydrodiol is catechol. The other minor isozyme that was studied does not oxidize (S)-1-indanol, but does oxidize dihydrodiols to catechols. The main activity for these enzymes is the reduction of nitrobenzaldehydes [F388].

Rabbit liver cytosolic enzyme is not separable from 3-hydroxyhexobarbital dehydrogenase, and like the monkey enzyme the specificity is broad [A2032].

Oestradiol 17a-dehydrogenase (E.C. 1.1.1.48)

Rabbit liver enzyme (see oestradiol 17b-dehydrogenase) oxidizes 17a-oestradiol and its 3-glucuronide [A157]. Chicken liver enzyme is marginally active towards 17a-oestradiol [B748].

Oestradiol ^-dehydrogenase (E.C. 1.1.1.62)

17b-Oestradiol i oestrone

Human ovary enzyme, optimum pH 8.1 and 6.9 for the forward and reverse reactions respectively, is cytosolic, with NADP(H), or less effectively NAD(H) as cofactors for reduction; 3-methoxyoestrone and 3-methoxy-17b-oestradiol are better substrates than the parent compounds [A3086].

Human endometrium enzyme utilizes NAD(P) +; reduction is not stimulated by

NADPH [A732]. Its activity increases at the end of the proliferation phase of the oestrus cycle, reaches its maximum value by the mid-secretory phase and falls towards its original value at the end of this phase. It then remains constant at about 5 per cent of the maximum value throughout the proliferative phase [A1104].

Human enzymes, both foetal and maternal, have an optimum pH of about 9, and are very unstable at — 20° [A 1551]. The reverse reaction, which is catalyzed by placental enzyme, is inhibited by ATP, especially with NADPH as cofactor. In contrast, ATP inhibition is more marked with NADH when 16a-hydroxyoestrone is the substrate [A1775]. Placental enzyme activity is not affected by prostaglandins [A374]. Kidney enzyme oxidizes 17b-oestradiol and its 3-sulphate and glucuronide conjugates [A1214]. Both human and rat erythrocyte enzymes reduce oestrone and its sulphate conjugate [A518].

Rabbit liver enzyme oxidizes 17a- and 17b-oestradiol and their 3-glucuronides. Soluble enzymes have been separated into three fractions. One, that oxidizes both 17a-compounds, has been further separated into five sub-fractions by isoelectric focussing, each of which exhibits different kinetics. The second fraction oxidizes 17b-oestradiol, and the third 17b-oestradiol-b-d-glucuronide [A157].

Sheep ovary 17b-hydroxysteroid: NAD(P) + dehydrogenase has a molecular weight of 70 000 and optimum pH 9.2 [A2389].

Rat liver microsomal enzyme reduces 16a-chlorooestrone; oestrone is inhibitory [A1749].

Chicken liver enzyme is composed of three isozymes, pI 6.0, 6.8 and 6.9, and optimum pH 9.9 for the forward reaction. Two isozymes have molecular weights of 43 000 and 97 000. The reaction requires NADP +; the reverse reaction utilizes NADPH. 17a-Oestradiol is marginally active, but oestriol is not a substrate. p -Chloromercuribenzoate is inhibitory [B748].

Cochliobolus lunatus enzyme acts on oestrone and alkyl steroids as well as quinones, aldehydes and ketones [K378].

Flavanone reduction (E.C. 1.1.1.234)

Flavanone 0 hydroxyflavan

Cryptomeria japonica enzyme is cytosolic, molecular weight 133 000 and optimum pH 7. It requires NADPH with ( )-aromadendrin and (+)-dihydroquercetin as substrates [E758].

Matthiola incana flower enzyme, optimum pH about 6, requires NADPH; NADH is not so good. It reduces (+)-aromadendrin to 3,4-cis-3,4,4?,5,7-pentahydroxyflavan; it also reduces ( )-dihydroquercetin and ( )-dihydromyricetin [D782].

Dihydrokaempferol 4-reductase (E.C. 1.1.1.219)

Matthiola incana flower enzyme, optimum pH about 6, forms cis-3,4-leucopelargonidin from dihydrokaempferol. Other substrates are ( )-dihydroquercetin and ( )-dihydromyricetin [D782].

Codeinone reductase (E.C. 1.1.1.247)

Papaver somniferum enzyme, a monomer molecular weight 35000 requires NADPH for reduction of ( )-codeinone and a range of morphinan ketones, but does not act on other aldehydes and ketones [K756, K757].

Naloxone reductase (E.C. 1.1.1.128)

Rat liver enzyme, molecular weight 34 000 and pI 5.9, which reduces naloxone to 6b-naloxol, is identical to 3a-steroid dehydrogenase. It also reduces benzaldehydes, acetophenones, quinones and non-aryl ketones [J744]. In guinea pig the 6a-isomer is formed [F579].

Daunorubicin reductase

Human liver contains four isozymes, three with optimum pH 6.0, and the fourth, possibly an aldehyde reductase, optimum pH 8.5. Their molecular weights are in the range of 30000-40 000 [C531]. Two isozymes of human brain aldehyde reductase reduce daunorubicin, pI 5.3 and 7.9 [B569].

Rabbit liver contains two reductases with optima at pH 6.0 and 8.5. Their properties indicate that they are ketone reductase and aldehyde reductase respectively [B402]. One, tentatively identified as E.C. 1.1.1.2, reduces daunorubicin less well than other substrates. Sodium chloride activates, with maximal activity at an ionic strength of 0.4, but it causes less activation at higher concentration. Sodium sulphate inhibits at ionic strength 1, but it activates at low concentration [A2007]. In one study only two of seven carbonyl reductases (E.C. 1.1.1.184) examined, pI 4.9 and 6.0 6.3, reduced daunorubicin [A3950].

Rat liver enzyme, molecular weight 39 000, pI 6.3 and optimum pH 8.5 9.0, is probably monomeric and requires NADPH. It also reduces some sugar aldehydes and straight chain aldehydes. The amino acid composition has been determined [A50, A1327].

Two classes of reductase found in both human and rabbit liver have optima at pH 6.0 and 8.5, whereas in mouse and rat liver the optimum pH is 8.5. These activities can be further separated by isoelectric focussing: Rabbit 'pH 6.0' enzyme: molecular weight 32300, 3 isozymes, pI 4.8, 5.3 and 6.3; 'pH 8.5' enzyme: molecular weight 36000, 2 isozymes, pI 5.9 and 6.3, with numerous minor forms in both classes. Human 'pH 6.0' enzyme: molecular weight 34 500; 'pH 8.5' enzyme, molecular weight 38 700; these are less clearly separated into isozymes than rabbit enzyme. Relative to rabbit, the activities in mouse, rat and man are very low. Adriamycin is also a substrate for human and rabbit enzymes, molecular weights 34 500 (man) and 32800 (rabbit). In man, the isozymes are similar to daunorubicin reductases with four isozymes, all with pI 5.4, as well as a number of minor isozymes [B169].

Steffimycinone reductase

This reaction, which occurs in Streptomyces nogalacter, forms steffimycinol with an optimum at pH 7. It requires NADPH; NADH is inactive [A2759].

Salutaridine reductase (E.C. 1.1.1.248)

Papaver somniferum enzyme, molecular weight 52000, pI 4.4 and optimum pH 6.0-6.5 (reverse reaction pH 9.0-9.5), forms (7S)-salutaridinol, a precursor of morphine. It is highly specific [K758].

Other ketone reductases

Rabbit liver enzyme, which is cytosolic, molecular weight 33 000 and optimum pH 6.2, requires NADPH. It reduces aryl ketones as well as alkyl ketones such as 2-(4-(2-oxocyclopentyl-methyl)phenyl)propionate [D125].

Aldehyde dehydrogenases (E.C. 1.2.1.3, 1.2.1.4, 1.2.1.5, 1.2.1.7, 1.2.1.28, 1.2.1.29, 1.2.1.39)

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