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Biomedical subjects

J M Ramirez

Publications and source records attributed to J M Ramirez.

70 records · Page 4Linked to original sources
PubMed1980

The photoreaction center of Rhodospirillum rubrum mutant strain F24.1.

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665-670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7-8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7-8% of typical photoreaction center.

Bacterial Chromatophores↗
PubMed1979

Regulation of cyclic photophosphorylation in Rhodospirillum rubrum by the redox state of nicotinamide-adenine dinucleotide.

We have investigated the effect of the redox state of added NAD on the rates of anaerobic cyclic photophosphorylation which are supported by membrane vesicles isolated from Rhodospirillum rubrum. As the redox potential of NAD was lowered, the activity decreased according to a typical potentiometric titration. The Nernst plot showed an apparent midpoint potential (E'o) of -350 mV and had a slope which corresponded to a two-electron transition. Besides, an almost identical potentiometric relationship was found to exist between the extent of light-elicited ATP formation in anaerobic suspensions of intact R. rubrum cells and the redox potential of intracellular NAD. These results suggest that physiological photophosphorylation in R. rubrum requires the oxidized form of a membrane-bound constituent (E'o = -350 mV) whose redox state is controlled by the redox state of cytoplasmic NAD.

Anaerobiosis↗
PubMed1979

Forebrain lesions and food intake in pigeons.

Thirty pigeons were randomly assigned to one of four groups: those receiving bilateral ablation of the archistriatum, the neostriatum, the nucleus stria terminalis, or those receiving a sham operation. All groups showed a non-significant temporary postoperative decrease in food intake, a non-specific effect attributed to the surgery. However, the duration of the hypophagia in the archistriatum- and nucleus stria terminalis-ablated groups was slightly longer (four weeks instead of three). A slight increase in body weight occurred in the nucleus stria terminalis-lesioned group, in spite of decreased food intake. These results, especially that there is no persistent hypophagia following archistriatum and nucleus stria terminalis lesions, are discussed in relation to the suspected role of several forebrain structures in feeding behavior.

Amygdala↗
PubMed1977

Photooxidase system of Rhodospirillum rubrum. I. Photooxidations catalyzed by chromatophores isolated from a mutant deficient in photooxidase activity.

The aerobic photooxidations of reduced 2,6-dichlorophenolindophenol and of reaction-center bacteriochlorophyll (P-870) have been investigated in membrane vesicles (chromatophores) isolated from a non-phototrophic Rhodospirillum rubrum strain. In aerobic suspensions of wild-type chromatophores, continuous light elicits an increase of the levels of 2,6-dichlorophenolindophenol and of oxidized P-870, which reach steady-state values shortly after the onset of illumination. In contrast, light induces in mutant suspensions a transient increase of the levels of 2,6-dichlorophenol-indophenol and of oxidized P-870, which fall to low steady-state values within a few seconds. These observations suggest that the mutation has altered a redox constituent located on the low-potential side of the photochemical reaction center, between a pool of acceptors and oxygen. Since endogenous cyclic photophosphorylation is catalyzed by mutant chromatophores at normal rates, it appears that the constituent altered by the mutation does not belong to the cyclic electron-transfer chain responsible for photophosphorylation. However, the system which mediates the aerobic photooxidations and the cyclic system are not completely independent: endogenous photophosphorylation is inhibited by oxygen in wild-type chromatophores but not in mutant chromatophores; in addition, the inhibitor of cyclic electron flow, 2-heptyl-4-hydroxyquinoline-N-oxide, enhances the aerobic photooxidation of reduced 2,6-dichlorophenolindophenol by chromatophores from both strains. These results support a tentative branched model for light-driven electron transfer. In that model, the constituent altered in the mutant strain is located in a side electron-transfer chain which connects the cyclic acceptors to oxygen.

2,6-Dichloroindophenol↗
PubMed1977

Bone remodeling in periodontal lesions.

This study was designed to investigate sites of major alveolar bone formation as a result of resorption of the interdental crest in periodontal lesions. Bone samples were taken from twelve patients requiring surgery as part of their periodontal treatment. Tetracycline was used in all cases to label bone recently formed. The selected areas were periodontal pockets ranging in depth from 6 to 8 mm. The bone deformities were of crater-form configuration. The buccal and lingual plates were removed. Later, the dehydrated speciemns were embedded in bioplastic and cut to sections 70 mu thick. Controls were healthy pieces of bone taken from the same patient in unaffected areas. Yellow fluorescent tetracycline labeling was observed in both periosteal and trabecular bone. In the trabecular bone, labeling was exhibited in the lamella of some Haversian systems, away form the bone resorption. There was a direct relationship between bone resorption and bone apposition as seen by the presence of tetracycline in the buccal and lingual alveolar plates. Controls showed only minimal labeling. The results of this study have posed the question as to whether inflammation could be the stimulus in the reactivation of osteocytes or bone formation, in the buccal and lingual walls of the periodontal lesions.

Alveolar Process↗
PubMed1975

The control by respiration of the uptake of alpha-methyl glucoside in Escherichia coli K12.

The uptake of methyl alpha-D-glucopyranoside (alpha-MG) by Escherichia coli K12 was decreased by the addition of substrates which stimulated the rate of oxygen consumption by the cells. The inhibition, which occurred only at non-saturating concentrations of alpha-MG, was not the result of a stimulation of the rate of exit of intracellular alpha-MG, and was abolished by the presence of carbonyl cyanide m-chlorophenylhydrazone or sodium azide. Since those drugs inhibit energy conservation at the respiratory chain and did not alter significantly the rate of oxygen consumption under the conditions for the assay of alpha-MG uptake, it appears that the inhibition of the transport system by respirable substrates is mediated by some form of energy derived from respiration.

Azides↗
PubMed1975

An oral hygiene measurement system for possible research and clinical use.

A new hygiene index has been developed that it is felt better meets the requirements for individual patient analysis than other indices. Examiner subjectivity is reduced by scoring tooth surfaces as clean (0) or dirty (1), determining a percentage of "dirty" surfaces which then becomes the Hygiene Analysis Index. Tested on a group of dental students it appears to discriminate adequately between the various levels of mouth hygiene.

Dental Deposits↗
PubMed1975

Comparative toothbrush efficiency utilizing a new oral hygiene index.

Through the use of a newly developed Hygiene Analysis Index (HAI), nine toothbrushes were evaluated for plaque-removing efficiency in 11 dental students. Results indicate that brush selection is an individual matter with no one brush clearly superior to all others. Further study is necessary before definite conclusions can be made.

Dental Deposits↗
PubMedDate not supplied

[Acute transverse cervical myelitis following hepatitis B vaccination. Evolution of anti-HBs antibodies].

BACKGROUND: The cause and effect relationship between anti-HBV immunization using recombinant vaccine and the development of a neurological event, including flare-ups of multiple sclerosis, is a widely debated issue. CASE REPORT: A previously asymptomatic 16-year-old girl was a hyper-responder to anti-HBV vaccine. Subsequent to a booster shot of anti-HBV recombinant vaccine, she developed regressive acute cervical transverse myelitis with intrathecal oligochonal IgG secretion and a hypersignal on the MRI T2 sequences of the cord. DISCUSSION: The distinction between a first episode of multiple sclerosis or post-vaccinal acute myelitis in this case will depend upon subsequent course, but this observation points out the very high level of persistent post-vaccinal immunization which can be acquired by a hyper-responder.

Adolescent↗
PubMedDate not supplied

[ROC (receiver operating characteristics) curve: principles and application in biology].

Laboratory test's diagnostic performances are generally estimated by means of their sensibility, specificity and positive and negative predictive values. Unfortunately, these indices reflect only imperfectly the capacity of a test to correctly classify subjects into clinically relevant subgroups. The appeal to ROC (receiver operating characteristic) curve appears as a tool of choice for this evaluation. Used in the medical domain since the 60s, ROC curve is a graphic representation of the relation existing between the sensibility and the specificity of a test, calculated for all possible cut-off. It allows the determination and the comparison of the diagnostic performances of several tests. It is also used to consider the optimal cut-off of a test, by taking into account epidemiological and medical - economic data of the disease. Used in numerous medical domains, this statistical tool is easily accessible thanks to the development of computer softwares. This article exposes the principles of construction and exploitation of a ROC curve.

Adenocarcinoma↗