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].
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. 18.104.22.168)
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].
(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. 22.214.171.124)
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. 126.96.36.199)
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. 188.8.131.52)
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].
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