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Biomedical subjects

A Oliva

Publications and source records attributed to A Oliva.

At least 163 records · Page 9Linked to original sources
PubMed1981

[Possible regulatory role of 5'-methylthioadenosine on enzymatic methyl esterification of membrane protein].

In the present study the effect of 5'methylthioadenosine (MTA), a natural metabolite of S-adenosylmethionine (AdoMet), on the enzymatic methyl esterification of intact erythrocyte membrane proteins has been investigated. The thioether significantly affects the methylation process :50% inhibition being observable at 100 microM MTA. This inhibition is due to the action of MTA on the enzyme protein methylase II. Since MTA is present in micromolar amounts in the cells, the reported effect could be of physiological interest and suggests a new regulatory role of this AdoMet metabolite.

Adenine↗
PubMed1981

Determination of ovarian function using first morning urine steroid assays.

A new direct radioimmunoassay measuring ovarian steroid metabolites in small aliquots of urine has been evaluated. For this purpose urinary levels of estrone-3-glucuronide (E1G) and pregnanediol-3-glucuronide (PG) were correlated with plasma values of estradiol (E2) and progesterone (P), respectively, from days 5 to 24 of the cycle in 24 women with normal cycles. Urine samples were representative of 1) first morning voiding; 2) 24-hour collection; and 3) all voidings except for the first morning one. The correlation between urinary E1G and PG with plasma values of E2 and P was statistically significant for the 3 collections of urine. The first morning voiding is selected as the sample of choice to determine E1G and PG due to its ease of collection and its high correlation with plasma E2 and P levels (r = .60, P less than .001; r = .73, P less than .001, respectively).

Circadian Rhythm↗
PubMed1980

Mechanism of propylamine-transfer reactions. Kinetic and inhibition studies on spermidine synthase from Escherichia coli.

Spermidine synthase (EC 2.5.1.16) purified from Escherichia coli has been subjected to a kinetic analysis including initial velocity and substrate analogs inhibition studies. Evidence is reported for a ping-pong mechanism, indicating that a propylaminated form of the enzyme is an obligatory intermediate in the reaction mechanism. S-Adenosyl(5')-3-methylthiopropylamine exerts a competitive substrate inhibition by combining with the improper stable enzyme form, while putrescine does not show any inhibitory effect. In order to investigate the substrate binding sites, new sulfonium-deaminated analogs of S-adenosyl(5')-3-methylthiopropylamine have been synthesized and assayed as substrates and as inhibitors of the reaction. The replacement of the amino group of adenine, or propylamine moiety of the sulfonium compound by the hydroxyl group, or both, resulted in a complete loss of activity as substrate. On the other hand, the deaminated analogs exert a competitive inhibition with respect to putrescine. On the basis of these results and in analogy with methyltransfer reactions, three recognition sites for S-adenosyl(5')-3-methylthiopropylamine on propylamine transfer enzymes are proposed.

Binding Sites↗
PubMed1980

Gonadotropinic reserve in women affected by hyperprolactinemic amenorrhea.

The Authors have evaluated the hypophysis gonadotropic reserve after stimulation by synthetic GnRH (100 ng) in women affected by functional hyperprolactinemia and by prolactin-secreting adenoma. The LH response was significatively higher in women affected by functional hyperprolactinemia. The PRL values seem to have no influence on the gonadotropic reserve except for the cases in which The PRL levels were higher than 200 ng/ml. In all these cases a prolactinoma was present. The FSH response was similar in the two groups considered.

Adenoma↗
PubMed1979

Preparation and analysis of new sulfonium derivatives from S-adenosyl(5')-3-methylthiopropylamine.

The paper reports the preparation and the chromatographic separation of new deaminated analogs of S-adenosyl(5')-3-methylthiopropylamine, i.e. S-adenosyl(5')-3-methylthiopropanol and S-inosyl(5')(-3-methylthiopropanol. These compounds can be used as specific inhibitors of polyamine biosynthesis. It is also reported the characterization of new sulfonium compounds by U.V. spectrophotometry, thin layer chromatography, high voltage electrophoresis, hydrolysis to known fragments.

Onium Compounds↗
PubMed1979

Bromocriptine in the treatment of hyperolactinemic amenorrhea.

Thirty women with secondary amenorrhea and hyperprolactinemia were studied; galactorrhea was present in 25 of them, and 18 were infertile. Serum prolactin (PRL) levels were high in all cases, between 26 and 120 ng/ml. All women were treated with bromocriptine in increasing doses from 2.5 to 5.0 or 7.5 mg daily, according to the response obtained, for 4 months. In 27 patients a PRL determination was performed during treatment; values returned to normal (up to 20 ng/ml) in 23 women and remained high in 4. Galactorrhea disappeared in 21 of 25 women. Ovulatory menses were re-established in 17 patients (56.6%). Seven women became pregnant (38.8%), one of them after bromocriptine and clomiphene were given simultaneously in the same cycle. According to our results and a literature review the following conclusions may be drawn: (1) bromocriptine is a useful therapeutic tool for re-establishing menstruation and inducing ovulation in patients with the hyperprolactinemic-amenorrhea syndrome; (2) the association of bromocriptine and clomiphene could be the next step in the treatment of patients who fail to ovulate with bromocriptine alone.

Adolescent↗
PubMed1979

5'-Methylthioadenosine phosphorylase from Caldariella acidophila. Purification and properties.

The occurrence of 5'-methylthioadenosine phosphorylase in Caldariella acidophila, a thermophilic bacterium growing optimally at 87 degrees C, is reported. It represents the first example in prokaryotes of a phosphoryolytic cleavage of the thioether. The reaction products, purified by ion-exchange chromatography, have been identified as 5-methylthioribose-1-phosphate and adenine by several analytical procedures. The enzyme has been purified to homogeneity in 32% yield by using DEAE-cellulose and hydroxyapatite chromatography, gel filtration and isoelectric focusing. The enzyme shows a high degree of thermophilicity, its temperature optimum being at 93 degrees C; furthermore no loss of activity is observable after exposure for 1 h at 100 degrees C. The kinetic data indicate a sequential mechanism of the reaction. The apparent Km values are 0.095 mM for 5'-methylthioadenosine and 6.1 mM for phosphate. The specificity of the reaction is rather strict. Experiments performed with analogues of the substrate, i.e. 5'-methylthioinosine, 5'-dimethylthioadenosine sulfonium salt, 5'-n-butylthioadenosine, 5'-isobutylthioadenosine, 5'-isobutylthioinosine, adenosylhomocysteine, 5'-thioethanoladenosine, adenosine, indicate the relevance of the adenine amino group and the sulfur in thioether form in the binding to the enzyme protein.

Adenosine↗
PubMed1978

[5'-methylthioadenosine phosphorylase from Caldariella acidophila. 1. Purification and partial characterization].

5'-Methylthioadenosine phosphorylase has been isolated from C.acidophila, a thermophilic bacterium living in acid hot springs at temperatures ranging from 63 to 89 degrees C. The enzyme has been purified to homogeneity in 32% yield. The enzyme shows a high degree of thermophilicity, its temperature optimum being 93 degrees C in the in vitro assay. The enzyme is exceptionally stable; no loss of activity was observable after exposure for 1 h at 100 degrees C. The optimum pH is about 7,2, with one-half of the maximal activity occurring at pH 6 and 9. The apparent Km for the substrates are: 8,3 x 10(-5) M for MTA and 4,3 x 10(-4) M for phosphate ions.

Adenosine↗
PubMed1978

Substrate specificity of 5'-methylthioadenosine phosphorylase from human prostate.

5'-Methylthioadenosine phosphorylase was purified approx. 340-fold from human prostate by using affinity chromatography by Hg-coupled Sepharose. The enzyme, responsible for the breakdown of 5'-methylthioadenosine into adenine and methylthioribose 1-phosphate, was partially characterized. The apparent Km for 5'-methylthioadenosine is 25 microM. It is activated by thiols and shows an absolute requirement for phosphate ions. New analogues of 5'-methylthioadenosine were prepared and their activity as substrates or inhibitors of the reaction was investigated. The replacement of the 6-amino group of the adenine moiety by a hydroxy group, as well as the replacement of N-7 by a methinic radical, resulted in an almost complete loss of activity. Otherwise the replacement of sulphur by selenium, as well as that of the methyl group by an ethyl one, is compatible with the activity as substrate. The positively charged sulphonium group also prevents catalytic interaction with the enzyme. The inhibitory effect of 5'-methylthiotubercidin (competitive) and 5'-dimethylthioadenosine sulphonium salt (non-competitive) was also demonstrated. The reported results suggest three binding sites between the substrate and the enzyme.

Adenosine↗
PubMed1978

[5'-methylthioadenosine phosphorylase from the human prostate. 1. Purification and partial characterization].

5'-Methylthioadenosine phosphorylase has been purified approximately 340-fold in 20% yield from human prostate: the use of affinity chromatography by Sepharose-Hg has been found particularly advantageous. The enzyme has been partially characterized and an apparent Km of 2.5 x 10(-5) M has been calculated for 5'-methylthioadenosine. The reaction is activated by thiols and shows an absolute requirement for phosphate ions.

Adenosine↗