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S Maldonado

Publications and source records attributed to S Maldonado.

28 records · Page 2Linked to original sources
PubMed1998

Cooperative stabilization of a molten globule apoflavodoxin fragment.

We have destabilized apoflavodoxin by site-specific excision of its C-terminal helix. The resulting flavodoxin fragment (Fld1-149) is compact and monomeric at pH 7.0, with spectroscopic properties of a molten globule and a low conformational stability. To study if Fld1-149 is cooperatively stabilized, we have measured the equilibrium urea unfolding by fluorescence, circular dichroism, and size-exclusion chromatography. The three techniques produced coincident unfolding curves. Furthermore, the thermal unfolding seems also to be cooperative as the same temperature of half-denaturation is obtained using fluorescence and circular dichroism. Fld1-149 displays cold denaturation. The equilibrium properties of Fld1-149 demonstrate that molten globules lacking well-defined tertiary interactions can still be cooperatively stabilized and that cooperatively may appear in protein conformations of very low stability. This suggests that protein folding intermediates, can, in principle, be cooperatively stabilized.

Apoproteins↗
PubMed1998

Apoflavodoxin: structure, stability, and FMN binding.

Flavodoxins are one domain alpha/beta electron transfer proteins that participate in photosynthetic reactions. All flavodoxins carry a molecule of flavin mononucleotide (FMN), non-covalently bound, that confers redox properties to the protein. There are two structurally distinct flavodoxins, short ones and long flavodoxins; the latter contain an extra loop with unknown function. We have undertaken the study of the stability and folding of the apoflavodoxin from Anabaena (a long flavodoxin) and the analysis of the interaction between the apoflavodoxin and FMN. Our studies indicate that apoflavodoxin folds in a few seconds to a form that is competent in FMN binding. The stability of this apoflavodoxin is low and its urea denaturation can be described by a two-state mechanism. The role of the different parts of the apoflavodoxin in the stability and structure of the whole protein is being investigated using mutagenesis and specific cleavage to generate apoflavodoxin fragments. The X-ray structure of apoflavodoxin is very similar to that of its complex with FMN, the main difference being the conformation of the two aromatic residues that sandwich FMN in the complex. In apoflavodoxin these groups interact with each other so closing the FMN binding site. Despite this fact, apoflavodoxin binds FMN tightly and rapidly, and the resulting holoflavodoxin displays a high conformational stability. We have found that one role of the aromatic residues that interact with FMN is to help to retain bound the reduced form of the cofactor whose complex with apoflavodoxin is otherwise too weak.

Anabaena↗
PubMed1996

[Preoperative and postoperative chemotherapy of osteogenic sarcoma of the limbs in children].

BACKGROUND: A preoperative and postoperative chemotherapy regimen was applied to nonmetastatic osteosarcoma of the extremities in patients under 16 years of age to prevent the progress to metastatic disease and reduce the volume of the primary tumor in order to assess a conservative surgery. PATIENTS AND METHODS: A modified T-10 chemotherapy regimen was used before surgery, including high dose methotrexate, vincristine, bleomycin, cyclophosphamide and dactinomycin. After surgery patients with a grade of tumor necrosis > 90% received the same regimen up to 45 weeks of treatment. For the cases with necrosis < 90%, this regimen was substituted by adriamycin and cisplatinum. Survival was studied in relation with age, sex, tumor site, levels of alkaline phosphatase and LDH, surgical treatment and tumor necrosis in the surgical specimen after preoperative chemotherapy. Uni and multivariate analysis were performed. RESULTS: Twenty seven patients with ages ranging from 5 to 15 years (median 11 years) were treated. The most common site of primary tumor was femur, followed by humerus and tibia. In 9 cases (33%) tumor necrosis was > 90%. Consecutive surgery was performed in 20 patients and 7 suffered amputation or disarticulation of the extremity. Twenty patients remain alive and disease-free at a median follow-up of 84 months. The probability of disease-free survival at 50 months is 71%. The only factor which influenced significantly the survival was the grade of tumor necrosis. Survival was 100% for the 9 patients with necrosis > 90% and 53% for the 18 cases with necrosis > 90% (p = 0.022). CONCLUSIONS: Preoperative and postoperative chemotherapy achieve disease-free survival in more than two thirds of patients with nonmetastatic osteosarcoma of the extremities and allow a non mutilating surgical treatment in the majority of them.

Adolescent↗
PubMed1995

Male gonadal function after chemotherapy in survivors of childhood malignancy.

Investigations of adult patients have shown that chemotherapy causes gonadal damage, but much less information is available about the impact of chemotherapy on gonadal function in children with malignant disease. At one time, being prepubertal during therapy was thought to confer some protection against chemotherapy induced gonadal damage. However, recent studies have indicated otherwise. We designed this study to assess gonadal function in 15 postpubertal males who had received polychemotherapy for a malignant disease during childhood and we compared them with 13 control adults males. The mean age of the patients at the time of the study was 18.2 +/- 3.6 years (range 13.8-29.0), and when given chemotherapy treatment was 10.2 +/- 3.0 years (range 6-16). At that time 12 were prepubertal and at the time of the study all were Tanner V. The mean interval from the completion of treatment until the study was 6.42 years (range 2.0-16.5). All patients had received polychemotherapy. We evaluated testicular size, sperm counts, LH and FSH after GnRH test, and testosterone levels. Puberty had progressed normally in all patients. We found no significant differences in testosterone and basal LH levels between patients and controls. However, we detected an appreciable difference in peak LH levels (P < 0.05) and in basal and peak FSH levels (P < 0.001). Seven patients had exaggerated LH response to GnRH, indicating dysfunction of the Leydig cells. The results of semen analyses were: 8 patients had azoospermia, 3 oligospermia, and 1 patient had a normal semen analysis. All patients with semen abnormalities presented a basal and peak FSH higher than the mean +2 SD of the control group. In summary, we found no evidence of gonadal protection in prepubertal patients. We found a high incidence of germinal cell damage, whereas Leydig cell abnormalities were found less often. An endocrine study of patients that have received chemotherapy is warranted.

Adolescent↗
PubMed1995

Agrammatism in Spanish: a case study.

This article presents a case study of a Spanish-speaking Broca's patient with a selective deficit in syntactic production. The analysis indicates difficulties in processing certain abstract categories such as clitic pronouns without any other significant morphological errors. This pattern and the abundant use of strong pronouns in subject position are accounted as a syntactic production deficit related to the computation of phonetically null elements e that enter in a syntactic chain. At the same time, the patient shows a milder problem in the production of canonical word order at the sentence level, which is also explained in syntactic terms.

Aged↗
PubMed1994

Antibodies to hepatitis C virus in human immunoglobulins: clinical meaning and diagnostic difficulties in children undergoing bone marrow transplant.

Anti-HCV antibodies were detected in 11 children undergoing BMT. All of them had received intravenous immunoglobulins (Ig) at a dose of 500 mg/kg every 2 weeks for the first 100 days post-BMT. Antibody titers appeared after the first dose and became undetectable between 1 and 6 months after the last dose of Ig. Detection of anti-HCV antibodies in these multitransfused patients raised doubts about their clinical significance. The clearance of antibody titers in the ensuing months, negativity of HCV RNA in the serum of the patients and the presence of anti-HCV in some batches of the commercial preparations administered supported the diagnosis of a passive transfer of antibodies and that true HCV infection could be ruled out. Routine screening of donors with the most sensitive tests and exclusion of anti-HCV positive sera from plasma pools should be mandatory. The presence of anti-HCV in these products has important clinical implications, leading to more expensive and time-consuming diagnostic procedures.

Bone Marrow Transplantation↗
PubMedDate not supplied

Development of angiotensin (1-7) as an agent to accelerate dermal repair.

Angiotensin II has been shown to be a potent agent in the acceleration of wound repair. Angiotensin (1-7), a fragment of angiotensin II that is not hypertensive, was found to be comparable to angiotensin II in accelerating dermal healing. This activity was evaluated in four models: rat and diabetic mouse full-thickness excisional wounds; rat random flap; and guinea pig partial thickness thermal injury. In all models, angiotensin (1-7) was comparable to angiotensin II. Angiotensin (1-7) accelerated the closure of wounds in diabetic mice and rats. In diabetic mice the resultant tissue at day 25 after injury was more comparable to normal tissue than the fibrotic scar observed in placebo-treated wounds. In the random flap model, angiotensin (1-7) was comparable to angiotensin II in maintaining flap viability (approximately 82%) and flap survival (40%). Finally, angiotensin (1-7) increased proliferation in the hair follicles at the edge of the wound and site of thermal injury, and the number of patent blood vessels on day 7 after partial thickness thermal injury. These data may be partially explained by the effect of angiotensin II and angiotensin (1-7) on keratinocyte proliferation. While platelet-derived growth factor had no effect on keratinocyte proliferation, angiotensin II and angiotensin (1-7) significantly increased keratinocyte proliferation. These data show that angiotensin(1-7) is comparable to angiotensin II in accelerating skin repair. Furthermore, the hypertensive and wound healing effects can be separated within the family of angiotensin peptides.

Angiotensin I↗
PubMedDate not supplied

A new cucurbitacin glycoside from Kageneckia oblonga (Rosaceae).

A novel cucurbitacin glycoside has been isolated from aerial parts of Kageneckia oblonga R. et P. and shown to be 3beta-(beta-D-glucosyloxy)-16alpha,23alpha-epoxycuc urbita-5,24-dien-11-one. The structure was established by usual spectroscopic and two-dimensional (2D) NMR techniques. This compound has found to be nontoxic when tested in-vivo cell culture assays. In previous investigations we reported 23,24-dihydrocucurbitacin F and prunasine. This was the first report on cucurbitacins from the genus Kageneckia (Rosaceae).

Animals↗