INVESTIGATIONS INTO THE POSSIBLE EFFECTS OF NATURALLY OCCURRING STEROIDS ON BIOSYNTHESIS OF 16-ANDROSTENES AND ANDROGENS IN MICROSOMES OF BOAR TESTIS

1981 ◽  
Vol 88 (3) ◽  
pp. 409-418 ◽  
Author(s):  
G. M. COOKE ◽  
D. B. GOWER
Keyword(s):  
Microsomal Fraction ◽  
Hydroxysteroid Dehydrogenase ◽  
Side Chain ◽  
Biosynthetic Pathways ◽  
Michaelis Constant ◽  
Ph Optimum ◽  
Naturally Occurring ◽  
Chain Cleavage ◽  
High Concentrations

The possible interactions between naturally occurring steroids and three enzymes of the biosynthetic pathways of 16-androstenes and androgens in the boar testis were investigated. High concentrations (1 mmol/l) of several steroids reduced the production of 5,16-androstadien-3β-ol when a microsomal fraction of boar testis was incubated with pregnenolone at pH 7·0 (the pH optimum of this reaction was found to be 6·6). When some of these inhibitors were investigated in more detail using Lineweaver–Burk analyses, the apparent inhibition constants, Ki, increased in value with increasing concentrations of inhibitors. When testosterone was added to 5,16-androstadien-3β-ol synthetase assays, the apparent Ki for 0·1 μmol testosterone/l was 0·165 μmol/l whereas those for 1·0, 10·0 and 100·0 μmol testosterone/l were 1·65, 16·5 and 48·7 μmol/l respectively. The apparent Michaelis constant, Km, of the reaction was 0·6 μmol/l. Similar results were obtained when oestrone, 17α-hydroxyprogesterone and 4,16-androstadien-3-one were added as effectors. At physiological concentrations, these steroids would not affect the biosynthesis of 5,16-androstadien-3 β-ol in vivo. Similarly, both 5α-androst-16-en-3β-ol, quantitatively the most important 16-androstene in the boar testis and 5,16-androstadien-3β-ol were examined for their effects on the 17α-hydroxy-C21 -steroid, C-17,20 lyase (C-17,20 lyase) and 17β-hydroxysteroid dehydrogenase (17β-OHSDH) enzymes of androgen biosynthesis. Neither of these enzymes was affected by the 16-androstene steroids even at concentrations of 100 μmol/l, and the apparent Km values were 3·3 and 26·0 μmol/l for C-17,20 lyase and 17β-OHSDH respectively. This lack of interaction between these pathways implies that the high levels of 16-androstene steroids produced by the testis will not interfere with androgen production, and also that the two side-chain cleavage steps from C21 precursors to C19 steroids are catalysed by independent systems.

Suppressed expression of the cytochrome P45017α protein in the testicular feminized (Tfm) mouse testes

1993 ◽  
Vol 139 (1) ◽  
pp. 127-NP ◽  
Author(s):  
C. Le Goascogne ◽  
N. Sananès ◽  
M. Gouézou ◽  
E. E. Baulieu ◽  
P. Robel
Keyword(s):  
Cytochrome P450 ◽  
Leydig Cells ◽  
Hydroxysteroid Dehydrogenase ◽  
Side Chain ◽  
Dibutyryl Cyclic Amp ◽  
Chain Cleavage ◽  
Left And Right ◽  
The Right ◽  
Old Mice

ABSTRACT The testes of testicular feminized (Tfm) mice synthesize and secrete abnormally low amounts of testosterone, as a consequence of selectively decreased cytochrome P45017α activity. To investigate the mechanism of this deficiency, three steroidogenic enzymes were immunolabelled in the testes of normal and Tfm adult (2·5–6 month old) mice. Cholesterol side-chain cleavage cytochrome P450 (P450scc) and Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) were detected in the Leydig cells of both normal and Tfm mice whereas, in contrast to normal mice, only a small proportion of Leydig cells were immunostained for cytochrome P450-17α-hydroxylase,C17→20 lyase (P45017α) in the testes of Tfm mice. The numbers of cells differed from male to male and interestingly were markedly higher in the right testis. Explants of testes from Tfm mice were kept in organ culture at 32 °C for 45 h, with or without dibutyryl cyclic AMP (100 or 500 μmol/l). All Leydig cells remained positive for P450scc and 3β-HSD, and P45017α became detectable in the majority of Leydig cells in both left and right testes, showing that the lack of expression of P45017α protein in Tfm mouse testes in vivo is not structural but is a regulatory phenomenon. Journal of Endocrinology (1993) 139, 127–130

Partial purification of galactinol synthase from leaves of Cucurbita pepo

1982 ◽  
Vol 60 (7) ◽  
pp. 1054-1059 ◽  
Author(s):  
John A. Webb
Keyword(s):  
Cucurbita Pepo ◽  
Partial Purification ◽  
Galactinol Synthase ◽  
Inositol 1 ◽  
Mature Leaves ◽  
Galactosyl Transferase ◽  
Naturally Occurring ◽  
High Concentrations ◽  
Uridine Nucleotides

An enzyme synthesizing galactinol, UDP-D-galactose:myo-inositol-1-α-D-galactosyl transferase (galactinol synthase), has been isolated and partially purified from mature leaves of Cucurbita pepo. The enzyme showed optimal activity between pH 7.5 and 8.0 and required Mn2+ and the presence throughout isolation, storage, and assay of a sulfhydryl protectant (β-mercaptoethanol). EDTA was completely inhibitory. From a range of metal ions only Mg2+ partially replaced Mn2+, while Co2+, Zn2+, Cu2+, and Ni2+ were inhibitory. The uridine nucleotides and UDP-glucose were from 40 to 80% inhibitory and probably constitute part of the in vivo control system. High concentrations of galactose, melibiose, and xylose were partially inhibitory. The enzyme appeared highly specific for myo-inositol and showed no ability for galactosyl transfer to any other naturally occurring sugar or sugar alcohol. Some reactivity was obtained with the isomeric scyllo-inositol but the product was not identified. A range of other sugar nucleotides were unreactive.

scholarly journals Mutant tryptophan aporepressors with altered specificities of corepressor recognition.

Genetics ◽  
1991 ◽  
Vol 128 (1) ◽  
pp. 29-35
Author(s):  
D N Arvidson ◽  
M Shapiro ◽  
P Youderian
Keyword(s):  
Dna Binding ◽  
Binding Pocket ◽  
Side Chain ◽  
Wild Type ◽  
Mutant Proteins ◽  
Naturally Occurring ◽  
Repressor Complex ◽  
Genes Encoding ◽  
Active Repressor

Abstract The Escherichia coli trpR gene encodes tryptophan aporepressor, which binds the corepressor ligand, L-tryptophan, to form an active repressor complex. The side chain of residue valine 58 of Trp aporepressor sits at the bottom of the corepressor (L-tryptophan) binding pocket. Mutant trpR genes encoding changes of Val58 to the other 19 naturally occurring amino acids were made. Each of the mutant proteins requires a higher intracellular concentration of tryptophan for activation of DNA binding than wild-type aporepressor. Whereas wild-type aporepressor is activated better by 5-methyltryptophan (5-MT) than by tryptophan, Ile58 and other mutant aporepressors prefer tryptophan to 5-MT as corepressor, and Ala58 and Gly58 prefer 5-MT much more strongly than wild-type aporepressor in vivo. These mutant aporepressors are the first examples of DNA-binding proteins with altered specificities of cofactor recognition.

Phytoestrogens

1998 ◽  
Vol 4 (1) ◽  
pp. 18-23 ◽  
Author(s):  
Rachel Mackey ◽  
John Eden
Keyword(s):  
Epidemiological Data ◽  
Asian Populations ◽  
Colon Cancers ◽  
Naturally Occurring ◽  
Urinary Levels ◽  
High Dietary Intake ◽  
High Concentrations ◽  
Relative Potencies

Phytoestrogens are defined as naturally occurring compounds found in plants that are structurally and functionally similar to 17-ß oestradiol or that produce oestrogenic effects. They are diphenolic in structure and are most commonly found in cereals, legumes and grasses. There have been numerous classes identified, the mostly highly investigated being isoflavones and lignans. Isoflavones are attenuated oestrogens. They behave both in vivo and in vitro as agonists and antagonists. Genistein and daidzein are found in high concentrations in soy beans and soy products. Their relative potencies as compared to oestradiol are low but they exhibit equivalent levels of bioactivity when tested in high concentrations. Lignans are found in oilseeds, cereals and berries. The main urinary lignans are enterolactone and enterodiol. Most phytoestrogens are modified by gut flora from glycoside precursors to a compound with oestrogenic properties. A high dietary intake of phytoestrogens was first noted to be associated with decreased incidences of certain diseases. This epidemiological data was obtained primarily from studying Asian populations. Soy consumption is highest in Japan, where urinary levels of phytoestrogen metabolites are extremely high and there are lower rates of so-called ‘Western’ diseases, including breast, endometrial, colon cancers as well as atherosclerotic disease. Research to date has focused on the antiproliferative potential of phytoestrogens, primarily genistein both in vitro and in vivo. Their role in the relief of menopausal symptoms, their hypocholesterolaemic effects and bone resorption protection have been investigated to some extent with promising results. A brief overview of the background of, and the research into, phytoestrogens will be provided in this article.

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