PubMed Health⌕ Search

Biomedical subjects

M C Nunes

Publications and source records attributed to M C Nunes.

9 recordsLinked to original sources
PubMed1999

In vivo nuclear magnetic resonance studies of glycolytic kinetics in Lactococcus lactis.

The metabolism of glucose by nongrowing cells of L. lactis strain MG5267 was studied under controlled conditions of pH, temperature, and gas atmosphere (anaerobic and aerobic) using a circulating system coupled to nuclear magnetic resonance (NMR) detection that allowed a noninvasive determination of intracellular pools of intermediate metabolites by 13C-NMR with a time resolution of 30 seconds. In addition, intracellular parameters, such as pH, NTP levels, and concentration of inorganic phosphate in the cytoplasm, could be monitored on-line by 31P-NMR with a time resolution of approx. 3 min. The time course for the concentrations of intracellular fructose 1,6-bisphosphate (FBP), 3-phosphoglycerate (3-PGA), and phosphoenolpyruvate (PEP), together with kinetic measurements of substrate consumption and endproducts formation, were used as a basis for the construction of a mechanistic model for glycolysis. In vivo measurements were complemented with determinations of phosphorylated metabolites in perchloric acid extracts. A top-down model was developed by simplifying the metabolism to the resolution allowed by the experimental data collected by in vivo NMR (grouped in seven metabolic steps). This simplified mechanistic model was adjusted to the metabolite concentrations determined by in vivo NMR. The results obtained led to the rationalization of the dynamics of glucose metabolism as being driven largely by ATP surplus. This excess causes accumulation of FBP due to NAD+ limitation, whose regeneration is dependent on downstream pyruvate reduction. The model was capable of predicting qualitative shifts in the metabolism of glucose when changing from anaerobic to aerobic conditions.

Glycolysis↗
PubMed1998

An interlaboratory study to find an alternative to the MPN technique for enumerating Escherichia coli in shellfish.

Nine laboratories in eight countries tested 16 batches of common mussels (Mytilus edulis) over a 32 week period in order to find an alternative to the Most Probable Number (MPN) technique to enumerate E. coli. The alternatives investigated included the 3M Petrifilm system, the Merck Chromocult agar method and a Malthus conductance technique. The Petrifilm was found to be unsuitable and was subsequently dropped from the trial. After 669 analyses, a correlation of 0.83 was observed for log E. coli counts between the MPN and Chromocult methods and there was no significant evidence that either method tended to give higher readings than the other. The MPN was slightly better than the Chromocult method for repeatability but the Chromocult was slightly better for reproducibility. However, the observed differences are probably too small to be of practical importance. On the basis of these data therefore, the two methods appear equally suitable for E. coli enumeration in shellfish. There were poor correlations between these methods and the Malthus technique. A small but significant number of samples tested positive on the Malthus instrument but were recorded negative on the MPN and Chromocult tests. Subsequent analysis positively identified E. coli from these Malthus assays. After statistical analysis, errors were noted in both the MPN and Chromocult methods but it was found that there would be no statistical differences if the Chromocult agar were used as an alternative to the MPN technique.

Colony Count, Microbial↗
PubMed1997

A novel pathway for the conversion of homocysteine to methionine in eukaryotes.

Activation of amino acid homocysteine was compared with that of methionine in rabbit crude liver extracts and purified multi-enzyme complex of aminoacyl-tRNA synthetases. Activation was studied by measuring the incorporation of radioactive amino acid into unlabelled trichloroacetic-acid insoluble materials in the absence of protein synthesis. Homocysteine synthetase activity was found in the crude extract and in the purified multi-enzyme complex of aminoacyl-tRNA synthetases. On a molar basis, the activation of methionine by the crude extract was five times higher than the activation of homocysteine. There was a partial loss of Hcy-tRNA synthetase activity in the purified multi-enzyme complex. Preliminary reconstitution experiments indicated a requirement for an additional factor for Hcy-tRNA synthetase activity. TLC of the amino acid released from tRNA charged with [14C]homocysteine, revealed radioactivity in homocysteine, methionine and homocysteine thiolactone, indicating a conversion of tRNA-attached homocysteine to methionine. Total tRNA was separated on a benzoylated cellulose column into a fraction enriched in initiator tRNA and a methionine-accepting, but initiator tRNA-deficient, fraction. Homocysteine-accepting activity was present only in the initiator tRNA-enriched fraction. Based on the above data we propose that homocysteine activation in reticulocyte lysates, reported previously, also occurs in liver. Activated homocysteine is attached to initiator tRNA and then converted to methionine by a methylating enzyme. In the absence of methylation, tRNA-attached homocysteine is hydrolysed to produce homocysteine thiolactone.

Animals↗
PubMed1984

Hyperprolactinemia in women with paternal deprivation during childhood.

It was reported that most females with prolactinoma, idiopathic hyperprolactinemia, or euprolactinemic galactorrhea were reared either without their father or with an alcoholic, violent father. To gain further insight into this association, a group of sisters of patients with prolactinoma (generally exposed to the same environment as the patients') and a control group were studied. Women with paternal deprivation during childhood differed from the women who had normal childhoods in that they had: 1) higher mean serum prolactin concentration (14.7 versus 9.4 ng/mL; P less than .001); 2) higher incidence of hyperprolactinemia (12 of 50 versus three of 59; P less than .005); and 3) higher incidence of galactorrhea (14 of 50 versus seven of 59: P less than .03). These observations support the contention that paternal deprivation during childhood is associated, in a minority of women, with a predisposition to develop hyperprolactinemia and presumably, prolactinoma later in life. A hypothesis on the possible mechanisms of a casual relationship is presented.

Female↗
PubMed1982

Hyperprolactinaemia and breast disease as evaluated by xeromammography.

This report compares the xeromammographic patterns of 35 patients with hyperprolactinaemia and 70 (age-matched) normoprolactinaemic controls. It is shown that nulliparous patients have less frequent mammary dysplasia and more patterns of involution than the nulliparous controls. The groups of parous patients and parous controls were similar to each other and both had more involutions and less dysplasia than the nulliparous controls. Hyperprolactinaemia in parous women is not associated with any changes in the xeromammographic breast patterns as compared to parous controls. The changes described in hyperprolactinaemic patients can be understood in terms of their low oestrogenic activity.

Adult↗
PubMed1981

Effect of treatment with bromocriptine on the size and activity of prolactin producing pituitary tumours.

Eleven consecutive patients with large prolactinomas were treated for 6 months with bromocriptine, (7.5 mg/day). Nine had invasion of the sphenoidal sinus, one a visual field defect and one a secondary trigeminal neuralgia. At the end of the treatment period 8 of the first 9 patients showed radiographical signs of bone remodelling and/or actual reduction of the tumour size. The last 2 patients had complete disappearance of their symptoms. The remissions could be observed as early as 3 weeks after the start of the treatment. Two patients suffered acute, reversible (partial in one case) episodes of loss of vision during the study. During the treatment the prolactin values decreased in all patients to an average of 1.7% of the baseline levels. There was a steep rise in the serum prolactin concentrations after withdrawal of the drug. After one month there was a plateauing at a high level, although lower than basal level. Libido and potency were restored in all 3 males studied. Two of the females experienced orgasm for the first time in their lives after some years of primary frigidity. It is concluded that bromocriptine reproducibly reduces the size of prolactinomas. This effect can be observed shortly after the beginning of the treatment and is at least partially reversible. Episodes of pituitary apoplexy may occur during the treatment of large tumours despite an otherwise favourable response.

Adult↗
PubMed1980

Psychosomatic factors in patients with hyperprolactinemia and/or galactorrhea.

A biographic and clinical investigation of 101 patients with hyperprolactinemia and/or galactorrhea is reported. Fifty-one patients were reared without their fathers and 18 with an alcoholic, violent one. These situations were uncommon in the control population, and the differences were statistically significant. There was a high frequency of complaints of obesity, headaches, frigidity, lightheadedness, and fullness of the abdomen, limbs, or face. There was a significant temporal correlation of external events in the natural history with onset or worsening of the symptoms. It is concluded that exposure during childhood to an environment characterized by an absent or alcoholic, violent father conditions some women to develop hyperprolactinemia and/or galactorrhea later in life as a response to specific environmental changes. These conclusions apply similarly to patients with prolactinoma, idiopathic hyperprolactinemia, and euprolactinemic galactorrhea, suggesting a close relationship among the 3 entities.

Family Health↗