Steroids and steroidases. XVIII. Micellar aggregation of Δ5-3-keto steroids lacking a polar C-17 group and its relation to the activity and specificity of the Δ5→ Δ4-3-ketosteroid isomerase of Pseudomonas testosteroni

Jb, Jones; Kd, Gordon

doi:10.1021/bi00725a013

Cited by 15 publications

(3 citation statements)

References 20 publications

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“…to 0.7 x 108M-1 * s-and since k-1 decreases from 1 lJx 10-4 to 5 x 10-4M-1* S-1, the k-l/k+, ratio is increased, resulting in a decrease in the efficiency parameter. The observations of the effect of increasing co-solvent concentrations on the k-1/k+, ratio is in agreement with the previously reported results with competitive inhibitors (Weintraub et al, 1972;Jones & Gordon, 1973).…”

Section: Non-labelled Substratesupporting

confidence: 93%

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Weintraub

Baulieu

Alfsen

1980

Biochemical Journal

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Studies of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Delta(4)-Delta(5)-isomerase with Delta(5(6))- and Delta(5(10))-steroid substrates demonstrate the importance of the position of the double bond for the efficiency of the isomerization process. Thus 3-oxo-Delta(5(6))-substrates have markedly high k(cat.) values, whereas those of 3-oxo-Delta(5(10))-substrates are very low and their apparent K(m) values approach equilibrium dissociation constants. The first step in the isomerization process is: [Formula: see text] which is governed by the k(-1)/k(+1) ratio and is shown to be very similar for the two classes of substrates (3-oxo-Delta(5(6))- and -Delta(5(10))-steroids). They therefore differ in the steps distal to the initial formation of the Michaelis-Menten complex. The use of the deuterated androst-5(6)-ene-3,17-dione substrate enabled us to calculate individual rate constants k(+1) and k(-1) as well as to determine the apparent rate-limiting step in the isomerization process. With the deuterated oestr-5(10)-ene-3,17-dione substrate, no significant isotope effect was observed suggesting that a different rate-limiting step may be operative in this isomerization process. Data are presented that indicate that under optimal concentrations of the efficient androst-5(6)-ene-3,17-dione substrate, the forward reaction for ES complex formation (as defined by k(+1)) is limited only by diffusion and the apparent K(m) does not approach the equilibrium constant, suggesting that the evolution of this enzyme has proceeded close to ;catalytic perfection'.

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Section: Non-labelled Substratesupporting

confidence: 93%

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Weintraub

Baulieu

Alfsen

1980

Biochemical Journal

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“…Since steroids are rather rigid molecules with only a few polar groups, with limited solubility in aqueous media, organic solvents are required for steroid solubilization over the extended steroid concentration range necessary to determine kinetic parameters quantitatively. The influence of different organic solvents on kinetic parameters has previously been described (Falcoz-Kelly et al, 1968;Weintraub et al, 1972;Jones and Gordon, 1973). The main effect observed with straight aliphatic alcohols is that the apparent affinity of substrates and steroid inhibitors as well as Vmax are progressively reduced, as the concentration of organic solvent is increased.…”

Section: Methodsmentioning

confidence: 99%

Interaction of steroids with Pseudomonas testosteroni 3-oxosteroid Δ4-Δ5-isomerase

Weintraub¹,

Vincent²,

Baulieu³

et al. 1977

Biochemistry

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“…That is, steroids are only weakly soluble in aqueous solutions (23). To test this possibility, we conducted a second experiment in which the assay conditions were the same as for the previous experiment except that the SP-DHT was added to the incubation medium in methanol (final concentration of methanol, 5%).…”

Section: Inhibition Of the Production Of E With Different Concentrationsmentioning

confidence: 99%

Inhibition of Hypothalamic Aromatase Activity by 5 Beta‐Dihydrotestosterone

Schumacher

Hutchison

1991

J Neuroendocrinology

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A variable amount of circulating testosterone that reaches brain cells is converted to biologically inactive 5/breduced metabolites, namely, 58-dihydrotestosterone (5D-DHT) and 5j-androstane-3a,l7 [i-diol (5[1,3a-diol). In avian species, the production of inactive 5/?-DHT and 5/j,3c(-diol is highest during embryonic and post-hatching life. In the present study, we have investigated the possibility that 58-reduction may not only correspond to a steroid inactivation pathway, but that 5B-reduced metabolites of testosterone may exert direct inhibitory effects on enzymatic pathways producing biologically active steroids. When added to hypothalamic homogenates prepared from adult male doves, 5B-DHT but not 5/,3a-diol inhibits the activity of the aromatase enzyme, which converts testosterone to 178-oestradiol. During the first days after hatching, when t h e production of 58-reduced metabolites is high, the hypothalamic aromatase is also inhibited by 5P-DHT. W e conclude that a high 5/i-reductase activity during sensitive periods for sexual differentiation may protect the avian brain from the differentiating effects of circulating androgens by inhibiting the production of oestrogen.The intracellular metabolism of testosterone (T) regulates the sensitivity of the brain to circulating hormone (1, 2). In the male hypothalamus, T is irreversibly converted into I7/i-oestradiol (E) and into 58-reduced metabolites such as S~-dihydrotestosterone (5j-DHT) and the corresponding 5/7-androstane-3a,l7P-diol (5/i,3a-diol) ( I ) . In contrast to aromatization, which leads to the production of behaviourally active E, S/breduction of T represents a major steroid inactivation pathway in brain cells. First, centrally administered 58-DHT is behaviourally ineffective. Second, 58-reduced metabolites do not accumulate in the cell nuclei of brain cells and are rapidly eliminated from hypothalamic cells ( I , 3). Thus, the action of T on the hypothalamus can be increased by producing more active E or decreased by producing more inactive SB-DHT. This is suggested by the observation that the activity of the hypothalamic aromatase is high in sexually active males (4). By contrast, an increased activity of the 5P-reductase enzyme has been associated with behavioural deficits ( 5 ) .In many avian species likc the dovc, the quail and the zebra finch, the production of 5b-reduced metabolites in the hypothalamus is about twenty times higher during embryonic and posthatching development than during adulthood (6-9). This high 58-reductase activity has been related to the reduced sensitivity of juvenile animals to the behavioural effects of T (10) and may protect the brain from the cffects of circulating androgens during sensitive periods for sexual differentiation (1 I). Thus, in avian species whcrc circulating oestrogcns masculinize thc male brain, high levels of 5P-DHT may protect the developing female brain from the masculinizing effects of circulating androgens ( I I , 12).By contrast, in avian species where circulating oestrogens demasculin...

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Steroids and steroidases. XVIII. Micellar aggregation of Δ5-3-keto steroids lacking a polar C-17 group and its relation to the activity and specificity of the Δ5→ Δ4-3-ketosteroid isomerase of Pseudomonas testosteroni

Cited by 15 publications

References 20 publications

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Interaction of steroids with Pseudomonas testosteroni 3-oxosteroid Δ4-Δ5-isomerase

Inhibition of Hypothalamic Aromatase Activity by 5 Beta‐Dihydrotestosterone

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