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B Tamaoki

Publications and source records attributed to B Tamaoki.

At least 55 records · Page 3Linked to original sources
PubMed1982

Kinetic mechanism of porcine testicular 17 beta-hydroxysteroid dehydrogenase.

A study on product inhibition of 17 beta-hydroxysteroid dehydrogenase from porcine testes was carried out by measuring the initial velocities of NADPH formation using testosterone as the substrate steroid. Type of inhibition by NADPH against NADP+ was competitive in both saturated and unsaturated concentrations of testosterone. In the saturated concentration of NADP+, activity of the enzyme was not inhibited by NADPH against testosterone. In the unsaturated concentrations of NADP+, however, NADPH brought mixed type inhibition against testosterone. The similar modes of inhibition by the product steroid, androstenedione were observed in the saturated and unsaturated concentrations of NADP+ and testosterone. The fluorescence of NADPH was increased in the presence of the enzyme, and fluorometric titration indicated that 1 mol of NADPH was bound to 1 mol of the 17 beta-hydroxysteroid dehydrogenase. Addition of testosterone to enzyme-NADPH complex reduced the intensity of fluorescence of NADPH, suggesting formation of testosterone-enzyme-NADPH complex as a ternary dead end complex. From the analyses of product inhibition and spectral changes of NADPH, the kinetic mechanism of the enzyme was revealed as rapid equilibrium random system with two dead end complexes which consisted of the two reduced reactants bound to the enzyme and the two oxidized ones bound to it.

17-Hydroxysteroid Dehydrogenases↗
PubMed1980

In-vitro synthesis of androgen from pregnenolone in the testes of the goat (Capra hircus) and identification of 5-pregnene-3beta,17alpha,20alpha-triol as an intermediate in the metabolic pathway of pregnenolone.

When [4(-14)C]pregnenolone was aerobically incubated in vitro in the presence of NAD+ and NADPH with cell-free homogenates of testicular tissue of adult domestic goats (Capra hircus), progesterone, 17alpha-hydroxypregnenolone, 17alpha-hydroxyprogesterone, 17alpha,20alpha-dihydroxy-4-pregnen-3-one, dehydroepiandrosterone, androstenedione and testosterone were identified as its known metabolites. Time-course studies on this metabolism showed that the production of 17alpha,20alpha-dihydroxy-4-pregnen-3-one and testosterone constantly increased up to the end of incubation, suggesting that these are both end-products of pregnenolone metabolism in this system. The other metabolites behaved as intermediates and were ultimately converted, in part, to testosterone by the testicular homogenates, indicating that testosterone was synthesized through both 4-ene and 5-ene-pathways. Furthermore, besides these metabolites, 5-pregnene-3beta,17alpha,20alpha-triol was also identified as an intermediary metabolite, formed from pregnenolone through 17alpha-hydroxypregnenolone in the presence of NADPH, and further convertible into 17alpha,20alpha-dihydroxy-4-pregnen-3-one by the microsomal fraction and into 17alpha-hydroxypregnenolone by the cytosol fraction in the presence of NAD+ and NADP+. It was not, however, significantly transformed into C19-steroids. Furthermore, 17alpha,20alpha-dihydroxy-4-pregnen-3-one, which was formed either from 5-pregnene-3beta,17alpha,20alpha-triol or from 17alpha-hydroxyprogesterone, remained almost unchanged without conversion to C19-steroids when incubated with the caprine testicular homogenates.

17-alpha-Hydroxypregnenolone↗
PubMed1979

Novel epimerization of steroidal allylic alcohols.

Epimerization of 4-pregnene-3 beta,20 alpha-diol into 4-pregnene-3 alpha,20 alpha-diol was achieved under the mild condition of an acidic medium at room temperature. This reaction was favorable for synthesis of 4-pregnene-3 alpha,20 alpha-diol in better yield, after chemical reduction of 20 alpha-hydroxy-4-pregnen-3-one with metal hydrides, which resulted in predominant production of 4-pregnene-3 beta,20 alpha-diol. The by-product which was formed more by raising the temperature was identified as 3,5-pregnadien-20 alpha-ol. This method was also applicable for epimerization of other delta 4-3 beta-hydroxysteroids.

Chemical Phenomena↗
PubMed1978

In vitro effect of 16alpha-hydroxyprogesterone on the enzyme activities related to androgen production in human testes.

Progesterone was converted in vitro to 16alpha- and 17alpha-hydroxyprogesterones in the presence of NADPH by the testicular microsomal fraction (precipitate at 10 000 x g-105 000 x g) obtained from patients with prostatic carcinoma. 16alpha-Hydroxyprogesterone was not metabolized by either the microsomal or the cytosol fractions, and accumulated in the incubation medium. 16alpha-Hydroxyprogesterone competitively inhibited the activity of the C-17-C-20 lyase in the testicular microsomal fraction with an estimated inhibitor constant of 72 micron. Moreover, the 16alpha-hydroxyprogesterone non-competitively inhibited the activity of the 20alpha-hydroxysteroid dehydrogenase in the testicular cytosol fraction and had an estimated inhibitor constant of 52.9 micron. Other testicular enzymes related to steroid metabolism, such as delta5-3beta-hydroxysteroid dehydrogenase coupled with the delta4-delta5 isomerase, 16alpha-hydroxylase, 17alpha-hydroxylase, and 17beta-hydroxysteroid dehydrogenase were not influenced in vitro by 16alpha-hydroxyprogesterone at the concentration of 0.1 mM. From these findings, it is concluded that 16alpha-hydroxyprogesterone inhibit specifically the cleavage of the side-chain of 17alpha-hydroxypregnenes in the course of androgen formation from pregnenolone in vitro.

Androgens↗
PubMed1977

Formation of a steroidal allyl alcohol in the mammary glands of mice.

After incubation of [4-14C]progesterone with cell-free homogenates of mouse mammary gland in the presence of NADPH, [14C]-labeled 4-pregnene-3alpha, 20alpha-diol was identified as a metabolite, besides 20alpha-hydroxy-4-pregnene-3-one which was the major metabolite.

20-alpha-Dihydroprogesterone↗
PubMed1976

Some aspects on pituitary function in human and rat anovulatory cycles.

To investigate the anterior pituitary function of human anovulatory cycles, hormonal environments were analyzed in an animal experimental model and women with anovulatory cycles. A specific antiserum to hypothalamic luteinizing hormone-releasing factor (LH-RF) was prepared in rabbits. Intravenous injection of 1.0 ml of this antiserum to 4-day cycling female rats on the proestrous day blocked ovulation in the following cycles without changing regular estrous cycles on vaginal smear. Thus experimental anovulatory cycles were induced in antiLH-RF serum-treated rats. In this experimental model, LH surge on the proestrous evening was blocked but LH and FSH were maintained at the basal levels. In human anovulatory cycles, serum LH and FSH levels were also not significantly reduced except during the period of LH surge, and blood estradiol-17beta levels were similar to the levels of women with normal ovulation. Serum progesterone levels were higher in the normal women after the expected day for ovulation. These data may indicate that the anterior pituitary is able to secrete its gonadotropins without stimulation by LH-RF and this tonic discharge of gonadotropins would maintain the basal levels of ovarian secretion of steroids.

Adult↗