PubMed Health⌕ Search

Biomedical subjects

J Ramírez

Publications and source records attributed to J Ramírez.

At least 109 records · Page 6Linked to original sources
PubMed1988

Relationships among iron absorption, percent saturation of plasma transferrin and serum ferritin concentration in humans.

The percent absorption of iron from four dietary sources was compared in 2018 human subjects with three indicators of iron status, serum ferritin concentration, percent saturation of plasma transferrin and iron absorption from a reference dose of ferrous sulfate. Higher correlation coefficients (r) were obtained by comparing dietary iron absorption with the reference dose absorption rather than with serum ferritin; for example, r = +0.61 and r = -0.38, respectively, for a meat and vegetable meal. However, in practice serum ferritin is almost as efficient as the reference dose absorption in estimating dietary iron absorption, because the 95% confidence limits calculated from the regression equations were very similar. The values of r calculated for iron absorption versus transferrin saturation were comparable to those obtained with the other indicators only in the range of transferrin saturation values below 25%, whereas in more iron-replete subjects (transferrin saturation greater than 25%), this correlation virtually disappeared. This indicates that, although both serum ferritin and transferrin saturation reflect iron status in iron-depleted subjects, the control of iron absorption in iron-replete subjects is more dependent on iron stores as reflected in the serum ferritin concentration than the percent saturation of transferrin.

Diet↗
PubMed1987

Electrochemical potential and ion transport in vesicles of yeast plasma membrane.

Vesicles from yeast plasma membrane were prepared according to Franzusoff and Cirillo [1983) J. Biol. Chem. 258, 3608), with slight modifications. When Mg-ATP was added, this preparation was able to generate a membrane potential, that was sensitive to inhibitors of the yeast H+-ATPase and uncouplers, and could be decreased by the addition of permeant anions, as measured by the fluorescence changes of the dye oxonol V. The addition of ATP could also generate a pH gradient, detectable by the fluorescence changes of the monitor aminochloromethoxyacridine. This gradient was sensitive to inhibitors of ATPase and uncouplers, and could be increased by the addition of permeant anions to the incubation mixture. When the vesicles were loaded with KCl, an increased rate of K+ efflux was produced upon the addition of ATP. Cytochrome oxidase from bovine heart could be reconstituted into the vesicles and was shown to generate a membrane potential difference, negative inside, evidenced by the fluorescence quenching of the cyanide dipropylthiacarbocyanine and the uptake of tetraphenylphosphonium. Besides, in these vesicles, K+ and Rb+, but not Na+ or NH+4 could decrease the quenching of fluorescence and the uptake of tetraphenylphosphonium produced when the electron-donor system was present. In the vesicles in which cytochrome oxidase was incorporated, upon the addition of cytochrome c and ascorbate, the uptake of 86Rb+ could be demonstrated also. This uptake was found to be saturable and inhibited by K+, and to a lesser degree by Na+. The results obtained indicate that these vesicles are reasonably sealed and capable of generating and maintaining a membrane potential. The membrane potential could be used to drive ions across the membrane of the vesicles, indicating the presence and functionality of the monovalent cation carrier. The vesicles, in general terms seem to be suitable for studying transport of ions and metabolites in yeast.

Adenosine Triphosphate↗
PubMed1987

Variations on the "dilution" method for reconstituting cytochrome c oxidase into membrane vesicles.

A method for the rapid incorporation of cytochrome c oxidase into membranes has been developed. This method essentially consists of obtaining a preparation of the enzyme in which it is isolated and then dissolving it in a medium containing 0.5% of the detergent Tween 20, which gives a final concentration of 0.0125% after reconstitution. These studies revealed an optimal ratio of 1 microgram of enzyme to 5 mg of phospholipids. A similar optimal ratio was found when the amount of protein was varied. The optimum temperature was found to be 30 degrees C. Without a peak value being reached, it was found that the best reconstitution was obtained at pH 7.0-8.0. When measurements were performed either with a fluorescent cyanine (DiSC3) or by the uptake of tetraphenylphosphonium, it was found that the enzyme, with cytochrome c added to the outside, was capable of generating a membrane potential that was negative inside. Using the same procedure, the enzyme could also be reconstituted into vesicles of yeast plasma membrane. The procedure, then, seems adequate for incorporating cytochrome c oxidase into different kinds of membrane vesicles.

Animals↗
PubMed1987

Early metabolic effects and mechanism of ammonium transport in yeast.

Studies were performed to define the effects and mechanism of NH+4 transport in yeast. The following results were obtained. Glucose was a better facilitator than ethanol-H2O2 for ammonium transport; low concentrations of uncouplers or respiratory inhibitors could inhibit the transport with ethanol as the substrate. With glucose, respiratory inhibitors showed only small inhibitory effects, and only high concentrations of azide or trifluoromethoxy carbonylcyanide phenylhydrazone could inhibit ammonium transport. Ammonium in the free state could be concentrated approximately 200-fold by the cells. Also, the addition of ammonium produced stimulation of both respiration and fermentation; an increased rate of H+ extrusion and an alkalinization of the interior of the cell; a decrease of the membrane potential, as monitored by fluorescent cyanine; an immediate decrease of the levels of ATP and an increase of ADP, which may account for the stimulation of both fermentation and respiration; and an increase of the levels of inorganic phosphate. Ammonium was found to inhibit 86Rb+ transport much less than K+. Also, while K+ produced a competitive type of inhibition, that produced by NH4+ was of the noncompetitive type. From the distribution ratio of ammonium and the pH gradient, an electrochemical potential gradient of around -180 mV was calculated. The results indicate that ammonium is transported in yeast by a mechanism similar to that of monovalent alkaline cations, driven by a membrane potential. The immediate metabolic effects of this cation seem to be due to an increased [H+]ATPase, to which its transport is coupled. However, the carriers seem to be different. The transport system studied in this work was that of low affinity.

Adenine Nucleotides↗
PubMed1986

Heme, ferritin and vegetable iron absorption in humans from meals denatured of heme iron during the cooking of beef.

The iron absorption from heme, ferritin and vegetable foods was tested in 63 humans (10 males and 53 females). The iron absorption from heme in beef exposed to prolonged heating was markedly reduced, following the degree of denaturation of the heme. The iron absorption from ferritin was about 31% of the absorption of the reference dose when administered with meat alone, falling to 11% of the reference dose when administered in a meal containing meat and vegetable foods. The absorption of ferritin iron was less than half that of vegetable iron. The data confirm a previous proposal that ferritin forms part of a subgroup of the non-heme iron pool.

Animals↗
PubMed1986

Episodic laryngeal dyskinesia. Clinical and psychiatric characterization.

We have obtained physiologic and psychiatric evaluations on five subjects with episodic laryngeal dyskinesia (LD) and compared them with three patients with expiratory laryngeal stridor and asthma (ELS), and five with chronic asthma (CA). Laryngoscopy confirmed adduction of the vocal cords. Diminished inspiratory flow rates with an expiratory/inspiratory ratio of 1.5 to 3.3 was demonstrated by flow volume studies. Flows improved strikingly while breathing an 80 percent helium/20 percent oxygen mixture. Patients with LD showed varying degrees of depression and sought some form of secondary gain. A histrionic personality, conversion or factitious disorders are not an essential part of this syndrome. Tracheostomy may seldom be necessary in the managing of the acute crisis of LD. Reassurance, oxygen, intermittent positive pressure, and sedation may be sufficient. Mildly depressed patients decreased the frequency and severity of wheezing episodes after receiving reassurance and a clear explanation of ventilatory mechanics.

Aged↗