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Biomedical subjects

A Valencia

Publications and source records attributed to A Valencia.

At least 127 records · Page 7Linked to original sources
PubMed1989

Spectroscopical studies on the structural organization of the lectin discoidin I: analysis of sugar- and calcium-binding activities.

One of the common characteristics observed in different families of sugar-binding proteins is the presence of aromatic residues in the proximity of the functional sugar-binding site (Quiocho, F. (1986) Annu. Rev. Biochem. 55, 287-315). This general property has made these proteins a very appropriate subject for studies using intrinsic fluorescence assays. In the present report we have studied the sugar binding activity of the lectin discoidin I, using a fluorescence-monitored titration assay. The galactose binding has been estimated, with an affinity constant of 1.8.10(-7) M-1 in the absence of calcium. In the presence of 1 mM Ca2+, the Kd of galactose binding is lowered to 2.7.10(-8) M-1. Calcium binding, by itself, seems to occur as two components with Kd values of 10(-7) and 10(-6) M-1. From these data, and sequence comparison of discoidin I with other lectins, a general model for ligand binding has been proposed in which a sequence from position 176 to 188, together with another region close to an apolar tryptophan residue, most probably Trp-50, would participate in the calcium- and sugar-binding site(s) of this protein.

Acetylgalactosamine↗
PubMed1988

Conformational alterations detected by circular dichroism induced in the normal ras p21 protein by activating point mutations at position 12, 59, or 61.

Activation of the oncogenic potential of ras oncogenes occurs by point mutations at codons 12, 13, 59, 61, and 63 of the sequences that codify for its product, a 21-kDa protein designated as p21. This activation has been postulated by computer models as modifiers of the structure of the protein, which may alter its biochemical and biological activities. We have expressed in bacteria the normal ras p21 and five mutated p21 proteins with mutations at positions 12, 59, 61, 12 plus 59, and 12 plus 61. Purification was carried out by solubilization from bacterial pellets in 7 M urea and chromatography through a Sephadex G-100 column to obtain greater than 95% purified proteins. Circular dichroic (CD) spectra showed that the normal protein and that activated by substitution of Ala59 to Thr59 are very similar in their overall structure. By contrast, point mutations affecting either 12 or 61 residues substantially altered the structure of the proteins. When the parameters of Chen et al. [Biochemistry II, 4120-4131 (1972)] were applied to the CD spectra, both normal and thr59-mutated ras proteins showed a less organized structure than mutated proteins at position 12 or 61. Since the Thr59 mutant has more similar transforming activity than other activated proteins, but a GTPase activity similar to that of the normal protein, our results support the hypothesis that there is more than one mechanism of activation of the ras p21 protein. One of these mechanisms involves important structural alterations by point mutations at position 12 or 61 which reduce the GTPase activity of the protein. Another mechanism will be that induced by a substitution of Ala59 to Thr59 which does not substantially alter the protein conformation. A putative alternative mechanism for the activation of this mutant is discussed.

Cell Transformation, Neoplastic↗
PubMed1988

Developmental changes in the structural organization of the lectin discoidin I detected by limited proteolysis.

Digestion of discoidin I with several proteolytic enzymes reveals the existence of structural domains in this lectin. Significative differences have been detected in the pattern of fragments generated by V8 protease on discoidin I of various developmental situations. The changes observed can be related to the presence of various types of tetrameric structures in discoidin I. Together with the presence of different types of isoforms in vegetative vs. differentiated cells, the results presented here suggest the involvement of different structural organizations in discoidin I which can be related to the biological functions of this lectin.

Dictyostelium↗
PubMed1987

Spectroscopic studies on the structural organization of the lectin discoidin I: homologies with fibronectin.

The structure of the lectin discoidin I has been studied by circular dichroism and fluorescence spectroscopy. A positive ellipticity band at 224 nm is detected in the CD spectrum of discoidin I. The fluorescence spectra show a defined shoulder at 325 nm that through acrylamide quenching has been associated with a displaced tryptophan residue partly buried in the discoidin I molecule. This tryptophan could also be responsible for the 224 nm positive band of the CD spectrum. These spectroscopic characteristics of discoidin I indicate the existence of structural homologies with fibronectin, where the optical activity of aromatic chromophores has been associated with the positive ellipticity band at 227 nm. The CD adjust parameters and theoretical secondary structure predictions show that discoidin I is a molecule with a low content of alpha-helix and beta-strand and high content of beta-turn structures, similar to other lectins.

Circular Dichroism↗
PubMed1987

Interstitial parametrial implants in carcinoma of the cervix stage II-B.

This retrospective analysis has been undertaken to ascertain whether an improvement in results can be obtained in Stage II-B cervical carcinoma with the use of interstitial parametrial irradiation. Between September 1972 and March 1982, 43 patients were treated by conventional intracavitary irradiation. Nine patients at high risk for local recurrence underwent post-radiation hysterectomy. Since 1980, 45 patients were entered into a study using parametrial interstitial implants and no hysterectomy. Patients were not allocated randomly and the interstitial group contained a disproportionate number of patients with poor prognostic features. Mean follow-up for the conventional radiotherapy group was 80 months, and for the interstitial group was 42 months. Overall pelvic control and actuarial survival in the conventional radiotherapy group (84 and 75%, respectively) were similar (log rank p-value = .61) to that observed in the interstitial implant group (80 and 77%). Analysis of pelvic control rates showed no significant advantage for either treatment group when compared by the various prognostic factors. The frequency of complications, however, was significantly higher in the interstitially irradiated patients (21% vs. 7%, p = .044).

Adenocarcinoma↗
PubMed1986

Localization of the high affinity calcium-binding site on tubulin molecule.

Tubulin is a calcium-binding protein. Two different modes of interaction of calcium with tubulin have been described: a high affinity interaction to one or two binding sites and lower affinity interactions to several other binding sites. In the present study, we have used limited proteolysis of tubulin with trypsin, chymotrypsin, and subtilisin to localize the high affinity calcium-binding sites. Our results indicate that two sites are located in the carboxyl-terminal region of both tubulin subunits, and that tubulin deprived of its carboxyl-terminal region is able to polymerize in the presence of 0.5 mM calcium.

Amino Acid Sequence↗
PubMed1986

Effects of early postnatal gonadal steroids on the successive conditional discrimination reversal learning in the rat.

In the present study the existence of sex differences in the acquisition, retraining and reversal of a successive conditional discrimination learning (Experiment 1) and the role of the early postnatal gonadal steroids on these discrimination tasks (Experiment 2) were investigated. In Experiment 1 two groups of experimentally naive rats (males and females) were exposed to a black-white successive conditional discrimination task in a T-maze. No sex differences were found in the acquisition or retraining. However, in the reversal phase females made fewer errors and reached the discrimination criterion (90% of correct choices) sooner than males. In Experiment 2, the absence of sex differences in the acquisition or retraining phases and the existence of sexual dimorphism in the reversal period were confirmed. In addition, female androgenization and male orchidectomy, on day one after birth, reversed the direction of the sex differences found in the successive conditional discrimination reversal learning.

Androgens↗
PubMed1986

Effects of sex steroids on the development of the accessory olfactory bulb mitral cells in the rat.

The effects of postnatal (on day 1 after birth) male castration and female androgenization on accessory olfactory bulb (AOB) mitral cells population were studied. Control males showed a greater number of AOB mitral cells than females. Postnatal treatments abolished and inverted these differences. It is suggested that the population of AOB mitral cells is influenced by sex steroids during at least a postnatal period.

Animals↗
PubMed1986

Zoapatle. XII. In vitro effect of kaurenoic acid isolated from Montanoa frutescens and two derivatives upon human spermatozoa.

Zoapatle aqueous crude extract (ZACE) from Montanoa tomentosa has been used as an oral contraceptive in traditional Mexican medicine for centuries. Kaurenoic acid, as isolated from Montanoa frutescens, and the methyl esters of 15-hydroxy-dihydro-kaurenoic acid and 15-keto-dihydro-kaurenoic acid were tested in vitro on human sperm motility and viability. The estimated ED50 concentrations immobilization were 374, 126 and 58 micrograms/ml, respectively using 15 X 10(6) sperms/500 microliter. Kaurenoic acid and both of its derivatives displayed only weak to negligible capacity for killing human sperms.

Diterpenes↗
PubMed1986

Effects of sex steroids on the development of two granule cell subpopulations in the rat accessory olfactory bulb.

The effects of postnatal male castration on day 1 (D1) after birth and female androgenization on accessory olfactory bulb (AOB) light and dark granule cell populations were studied. Control males showed a greater number of both light and dark AOB granule cells than females. Postnatal treatment reversed these differences in the light granule cells. Female androgenization on D1 does not affect the number of AOB dark granule cells. However, male orchidectomy also on D1 significantly decreases the number of dark granule cells. Androgens injected into female rats are able to increase the number of AOB dark granule cells if they are administered on D14. This suggests a different critical period for the early effects of androgens on the dark granule cells with respect to light granule cells.

Animals↗
PubMed1985

The zoapatle. VII. Antiimplantation effect in the rat of zoapatle aqueous crude extract (ZACE) from Montanoa tomentosa and Montanoa frutescens.

Intrauterine administration of zoapatle aqueous crude extract (ZACE) from Montanoa frutescens on the fourth day of rat pregnancy, at concentrations equivalent to 50 mg and 5 mg of dry leaves, was associated with total inhibition of implantation sites. On the other hand, ZACE from Montanoa tomentosa equivalent to 50 and/or 100 mg of dry leaves, prepared and administered in the same fashion, did not inhibit the number of implants by day 11 of pregnancy. However, most implants were found abnormal, of blue color, poor orientation or spacing; these morphological changes could be considered as reabsorption sites.

Animals↗
PubMed1985

The zoapatle. IX. In vitro effect of Montanoa tomentosa and Montanoa frutescens upon human sperm and red cells.

The effect of zoapatle aqueous crude extract (ZACE) was further studied and partially characterized upon human and rabbit spermatozoa. ZACE prepared from Montanoa tomentosa s.s.p tomentosa did not influence sperm motility or viability in a wide range of ZACE concentrations tested; on the other hand, ZACE prepared from Montanoa frutescens had immediate and constant inhibitory effect upon motility and decreased cell viability. Red cell lysis was readily observed with ZACE-frutescens, but not with ZACE-tomentosa. The effect of time on ZACE-frutescens potency for inducing red cell lysis was observed.

Animals↗
PubMed1985

The zoapatle. X. The in vitro effect of zoapatle aqueous crude extract (ZACE) and histamine upon rat and guinea pig uterine strips.

In vitro histamine response in rat and guinea pig uterine strips was similar to the one observed with zoapatle aqueous crude extract (ZACE). The relaxing effect elicited by ZACE/tomentosa on the in vitro rat uterine strips was not mediated by activation of H-2 histamine receptors; moreover, the increase on uterine contractility elicited by ZACE/tomentosa on the in vitro guinea pig uterine strip was not mediated through the activation of H-1 histamine receptors.

Animals↗
PubMed1985

The zoapatle. XI. Effects elicited by Montanoa tomentosa and Montanoa frutescens on rat uterine strips.

Zoapatle aqueous crude extract (ZACE) obtained from Montanoa tomentosa (M.t.) inhibits the in vitro spontaneous contractility pattern of rat uterine tissue. The opposite effect was observed with ZACE from Montanoa frutescens (M.f.) in the same preparation. Both plant extracts, M.t. and M.f., increased the in vitro spontaneous contractility pattern in the uterine guinea pig assay. In depolarized uterine tissue, propranolol (beta-blocker) inhibited the relaxing effect induced by M.t.. Atropine (cholinergic antagonist) abolished the increase in uterus contractility produced by the presence of M.f.

Acetylcholine↗
PubMed1984

Effects of sex steroids on the development of the accessory olfactory bulb in the rat: a volumetric study.

The effects of postnatal (on day 1 after birth) male castration and female androgenization on accessory olfactory bulb (AOB) volume were studied. Control males showed greater values than females in AOB volume. Postnatal treatments abolished and inverted these differences. It is suggested that the AOB development is influenced by sex steroids during at least a postnatal period.

Animals↗
PubMed1984

Capacitation of human spermatozoa by heparin.

Zona-free hamster oocytes were incubated in vitro with human spermatozoa treated with heparin for 5, 10, 20, and 30 min. Sperm penetration was observed 2, 4, and 8 h after insemination. Sperm penetration was successful in 40%, 60%, and 69% of the oocytes treated for 10 min with heparin. Feminine and masculine pronuclei were clearly identifiable. In these samples, 80% of the sperm was alive and there was approximately 68% progress motility. Live sperm were observed for up to 24 h. Since glycosamineglycan sulfates are normally present in the ooplasm, zona pellucida, follicular and uterine fluids, this might suggest a direct participation of heparin in human sperm capacitation.

Animals↗
PubMed1983

Treatment of locally advanced cancer of the cervix with transperineal interstitial irradiation. Report on 106 cases.

The survival of patients with locally advanced cancer of the cervix (stage IIB, IIIB, and IVA) treated with conventional intracavitary radium remains unsatisfactory. Over 50% of these patients are local failures and die with uncontrolled tumor in the pelvis. In 1978, we began performing transperineal interstitial implants to the parametria in patients with advanced disease. One hundred six evaluable patients (34 IIB, 67 IIIB, and five IVA) received one (99) or two interstitial implants (7) following 40-50 Gy of external supervoltage external irradiation. In addition, seven patients underwent exploratory staging laparotomies concurrently with the first implant procedure. Mean follow-up is 23 months and range is 12-60 months. Control of the pelvic tumor has been documented in 85%, 75%, and 40% of stage IIB, IIIB and IVA patients, respectively. Seven patients developed distant metastases and three died of intercurrent disease with no evidence of pelvic relapse. Nineteen patients (18%) developed radiation-related complications: proctitis or cystitis (six), rectal stenosis (six), ulceration and necrosis of the vaginal wall (one), and recto- or vesicovaginal fistula (six). It is noteworthy that 7/11 patients (64%) who had radioactive sources placed on the surface of the vaginal obturator as a substitute for an intrauterine tandem developed severe complications. We conclude that transperineal interstitial irradiation is both safe and an effective modality in the treatment of advanced cancer of the cervix.

Brachytherapy↗