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Biomedical subjects

M Graber

Publications and source records attributed to M Graber.

At least 19 recordsLinked to original sources
PubMed2001

Alcoholysis catalyzed by Candida antarctica lipase B in a gas/solid system obeys a Ping Pong Bi Bi mechanism with competitive inhibition by the alcohol substrate and water.

The kinetics of alcoholysis of methyl propionate and n-propanol catalyzed by Candida antarctica lipase B supported onto silanized Chromosorb P was studied in a continuous solid/gas reactor. In this system the solid phase is composed of a packed enzymatic sample and is percolated by nitrogen as carrier gas, which simultaneously carries substrates to the enzyme while removing reaction products. In this reactor the thermodynamic activity of substrates and effectors can be perfectly adjusted allowing kinetic studies to be performed under different operating conditions. The kinetics obtained for alcoholysis were suggested to fit a Ping Pong Bi Bi mechanism with dead-end inhibition by the alcohol. The values of all apparent kinetic parameters were calculated and the apparent dissociation constant of enzyme for gaseous ester was found very low compared with the one obtained for liquid ester in organic medium, certainly due to the more efficient diffusion in the gaseous phase. The effect of water thermodynamic activity was also investigated. Water was found to act as a competitive inhibitor, with a higher inhibition constant than n-propanol. Thus alcoholysis of gaseous methyl propionate and n-propanol catalyzed by C. antarctica lipase B was found to obey the same kinetic mechanism as in other non-conventional media such as organic liquid media and supercritical carbon dioxide, but with much higher affinity for the substrates.

1-Propanol↗
PubMed2001

Bioavailability of US commercial magnesium preparations.

Magnesium deficiency is seen with some frequency in the outpatient setting and requires oral repletion or maintenance therapy. The purpose of this study was to measure the bioavailability of four commercially-available preparations of magnesium, and to test the claim that organic salts are more easily absorbed. Bioavailability was measured as the increment of urinary maginesium excretion in normal volunteers given approximately 21 mEq/day of the test preparations. Results indicated relatively poor bioavailability of magnesium oxide (fractional absorption 4 per cent) but significantly higher and equivalent bioavailability of magnesium chloride, magnesium lactate and magnesium aspartate. We conclude that there is relatively poor bioavailability of magnesium oxide, but greater and equivalent bioavailability of magnesium chloride, lactate, and aspartate. Inorganic magnesium salts, depending on the preparation, may have bioavailability equivalent to organic magnesium salts.

Adult↗
PubMed2000

Isolation, purification and partial amino acid sequence of a highly hydrophobic new microcin named microcin L produced by Escherichia coli.

We report here the production, by an Escherichia coli strain, of two microcins, microcin J25 and a new one that we designated microcin L. The active peptides were separated by solid phase extraction on C(18) cartridges. Microcin L was then purified to homogeneity by cationic-exchange high-performance liquid chromatography. Its molecular mass, determined by mass spectrometry, is 8899 Da. The amino acid composition and the sequence of the first 40 N-terminal residues indicate that microcin L is a hydrophobic peptide, which exhibits high homology to gassericin and lactacin F which both belong to the class II bacteriocins.

Amino Acid Sequence↗
PubMed2000

Idiopathic stabbing headache associated with monocular visual loss.

BACKGROUND: Idiopathic stabbing headache, which is a brief, sharp, severe jabbing pain that is confined to the head, responds well to treatment with indomethacin sodium. It may occur as a primary entity but more likely is associated with other types of headache, including migraine. SETTING: Emergency department of a teaching hospital. PATIENT: A 27-year-old man presented to the emergency department with stabbing, sharp pain in the right temporal area associated with complete of loss vision in his right eye. The patient had a history of migraine with aura since 1995. RESULT: The patient was treated with oxygen inhalation and indomethacin, with complete resolution of his symptoms. CONCLUSION: A case of idiopathic stabbing headache associated with monocular visual loss was relieved by oxygen and indomethacin therapy.

Adult↗
PubMed2000

Tesio catheter: radiologically guided placement, mechanical performance, and adequacy of delivered dialysis.

PURPOSE: Tunneled catheters are an alternative means of vascular access for patients in need of hemodialysis who cannot undergo dialysis through a surgical shunt. This study was undertaken to evaluate the performance of the Tesio dialysis catheter. MATERIALS AND METHODS: A prospective study of the Tesio catheter was performed. Follow-up data regarding catheter function and adequacy of dialysis were obtained from nine hemodialysis facilities. RESULTS: Seventy-nine Tesio catheters were placed in 71 patients. Immediate technical success was 99% (78 of 79 catheters). The procedure complication rate was 9% (seven catheters). Only two complications required intervention: one fatal air embolism and one chest wall hematoma. Sixty-seven catheters in 60 patients were followed up for a total of 4,367 catheter days. Overall, catheter-related infection occurred in 9% (six of 67 catheters). Primary catheter patency was 87% at 1 week, 82% at 1 month, 72% at 3 months, and 66% at 6 months. Mean blood flow was 286 mL/min immediately after insertion, 301 mL/min at 3 months, and 306 mL/min at 6 months. Adequate dialysis dose as reflected by a urea reduction ratio of 60 or more or a urea kinetic modeling, or Kt/V, value of 1.2 or more was observed on at least one occasion for 74% and 76% of catheters, respectively. CONCLUSION: The Tesio catheter is a reasonable means of vascular access for patients who undergo dialysis but are not candidates for surgical shunt placement.

Adolescent↗
PubMed2000

Nitric oxide: a greenhouse gas is used in the treatment of respiratory failure.

Medical science has long made the improbable probable, saving lives and improving quality of life. Upon the introduction of medical devices that can deliver safe quantities of the poisonous gas nitric oxide to help patients with respiratory and other illnesses, the FDA requested ASTM Committee F29 on Anesthetic and Respiratory Equipment to provide standards for these devices. Dr. Daniel Supkis and Mark Graber explain the delicate process of delivering NO to patients and how ASTM standards now in development will increase the safety of this procedure.

Humans↗
PubMed1997

Pseudopulmonary embolism: acute respiratory distress in the syndrome of heparin-induced thrombocytopenia.

A 73-year-old man with myasthenia gravis was treated with daily plasmapheresis. During the course of treatment, the patient developed progressive thrombocytopenia and an episode of severe acute respiratory distress suggesting pulmonary embolism. The thrombocytopenia and respiratory impairment improved after discontinuation of heparin, and both recurred on heparin rechallenge. The presence of heparin-specific antibodies was confirmed by in vitro assay. The time frame of clinical events suggests a heparin-mediated mechanism for both the thrombocytopenia and respiratory compromise. We conclude that acute respiratory distress may be the presenting manifestation of the syndrome of heparin-associated thrombocytopenia in patients treated with dialysis or apheresis.

Acute Disease↗
PubMed1997

Attitude of emergency department patients toward HIV-infected health care workers.

A telephone survey of a random sample of adult emergency department (ED) patients was conducted at a university health science center. The purpose of the study was to determine the opinion of ED patients concerning the risk of human immunodeficiency virus (HIV) transmission and their willingness to be treated by HIV-infected physicians and nurses. Surveys from 107 ED patients were compiled and available for analysis. Ninety percent of the respondents were tolerant of an HIV-infected physician or nurse (HIV + HCW)performing noninvasive procedures. Fifty percent were tolerant of an HIV + HCW performing invasive procedures. Twenty-six percent of the patients said they would leave the department rather than be treated by an HIV + HCW. Patients older than 50 years were less tolerant (P = .004) and more likely to leave the ED (P = .001).

Adolescent↗
PubMed1996

Ontogeny of vasoactive intestinal peptide gene expression in rat brain.

Vasoactive intestinal peptide (VIP) expression was studied during rat brain development using in situ hybridization histochemistry with a 48mer, S35-ATP-labeled probe. First expression of VIP was found in the lateral thalamus at E17, in a region later recognized as the reticular nucleus. At E19, VIP mRNA was also found in the hypothalamus, especially the suprachiasmatic nucleus. The only other prenatal localizations were the cortex and the brainstem. VIP expression continously matured during the first three postnatal weeks, and adult-like patterns were found at P22, when cerebral cortex, ventrolateral and reticular thalamic nuclei, suprachiasmatic nucleus were the regions with most prominent VIP expression. These results demonstrate the relatively late appearance of VIP gene expression in the rat forebrain as compared with peptides like SRIF and CCK, suggesting it does not have a major role in early brain maturation.

Amygdala↗
PubMed1995

The sonographic appearance of renal transplants during pregnancy.

This study evaluates the sonographic appearance of renal allografts during pregnancy. Baseline and intrapartum sonograms and serum creatinine levels from 19 women with 24 pregnancies were evaluated. In 15 of the 22 pregnancies with more than one examination, renal dilatation increased during gestation. The degree of dilatation was minimal to mild, with moderate dilatation present only in the third trimester. There were no cases of severe dilatation. Change in renal dilatation was seen in eight of eight patients with normal renal function, four of six patients with moderate renal impairment, and in zero of two patients with severe renal impairment. Normal transplant morphology or a single abnormal criterion was found in 23 of 24 pregnancies. Transplant morphology is not affected by pregnancy. Renal allografts in asymptomatic patients frequently demonstrate minimal to mild dilatation during pregnancy. The ability of the transplant kidney to dilate decreases with worsening renal function.

Adult↗
PubMed1995

Experimental and theoretical analysis of the chromatographic behaviour of protein purification fusions carrying charged tails.

Poly(glutamic acid) tail consisting of 6 glutamate residues was fused to the N-terminus of Escherichia coli beta-galactosidase (beta-gal), by genetic engineering techniques. The wild-type and modified genes were expressed intracellularly and in soluble state in Escherichia coli, leading to the proteins respectively designated beta-gal2 and E6-beta-gal. Both enzymes were purified by affinity chromatography. The specific activity of purified E6-beta-gal was found to be comparable to the wild-type enzyme and its increased net charge was indicated by lon-Exchange Chromatography (IEC). The use of such a charged fusion for selective recovery of beta-gal from cell extract using IEC and Ion-Exchange Membrane Chromatography (IEMC) was explored. The additional charges enabled the separation factor to be increased about two-fold on both IEC and IEMC, but the IEMC step achieved a better throughput than the IEC step. The selectivity of recovery promoted by the charged tail was further analysed by processing the experimental data obtained in IEC with the Stoichiometric Displacement Model, a recent model very appropriate for the understanding of the retention of polymeric biomolecules on ion-exchangers. It was shown that E6-beta-gal had the same characteristic charge as beta-gal2 but that the binding constant to the ion-exchanger of the tagged beta-gal was 6 times greater than for the wild-type enzyme.

Amino Acid Sequence↗
PubMed1994

Amidase activity and thermal stability of human thrombin.

Previous studies of amidase activity of human alpha-thrombin have yielded variable results and the decrease of this activity as a function of time and temperature has never been quantified. As this protease is an efficient tool in biochemistry and biotechnology thanks to its extreme selectivity, amidase activity and stability of thrombin were investigated with the synthetic substrate Tos-Gly-Pro-Arg-pNa. Enzyme activity as a function of temperature showed an optimum peak at 45 degrees C. The pH dependence of the activity showed a maximum around 9.5. The addition of NaCl promoted an increase of the activity. Stability of thrombin decreased rapidly when increasing the temperature from 25-45 degrees C and when diluting the enzyme. The presence of glycerol and ethylene glycol promoted a small increase of thrombin half life, whereas polyethylene glycol had a more pronounced positive effect even at very low concentrations.

Amidohydrolases↗
PubMed1993

A model of the hyperkalemia produced by metabolic acidosis.

In both humans and animals, mineral acids predictably result in hyperkalemia, whereas plasma K+ remains normal or may even decrease during organic acidosis. The purpose of these studies was to define the mechanism for these effects in the opossum kidney cell, an established epithelial cell line derived from the renal cortex of the opossum. This cell was chosen because the acid/base transport pathways in this cell type are well defined and because it is one of the few cells known to express K/H antiport, the transport pathway that has been proposed to mediate the hyperkalemia of acidosis. Cell K+ at pH 7.4 averaged 988 +/- 48 nmol/mg protein. Relative to this value (100%), cell K+ increased when buffer pH was increased to pH 8.4 with NaOH (108% +/- 3%) and decreased when buffer pH was acidified with HCl to pH 6.4 (93% +/- 4%), producing a highly significant correlation of cell K+ with buffer pH: cell K+ (% of baseline at pH 7.4) = 6.9 (cell pH) + 49 (r = 0.5, P < 0.004). In contrast, acidification of the buffer to pH 6.4 with either butyric or lactic acid increased cell K+ (115% +/- 4% and 110% +/- 2%, respectively, both P < 0.05 v 7.4 or HCl value). Cell pH acidified in response to HCl at a rate of 0.0053 +/- 0.0007 pH U/s, a significantly slower rate than in response to lactic acid or butyric acid (0.0071 +/- 0.0007 and 0.0091 +/- 0.0007 pH U/s, respectively). Unidirectional ouabain-sensitive 42K+ influx was significantly inhibited by HCl acidosis and less so by the organic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1993

Regulation of cell pH by K+/H+ antiport in renal epithelial cells.

Acid-loaded opossum kidney (OK) cells secrete H+ by Na+/H+ exchange and by a Na(+)- and HCO3(-)-independent pathway that has not been fully characterized. We studied the Na(+)-independent component by measuring H+ flux using the pH-sensitive trapped indicator 2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein. Two Na(+)-independent H(+)-transport systems were identified in acid-loaded cells perfused with HCO3(-)-free buffers. The minor component appears to be a conductive pathway for H+, over 90% inhibitable by 5 mM barium. The major component is stimulated by extracellular K+ and was fully active in the presence of barium, amiloride, ouabain, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and bumetanide and in the absence of Cl-. Ammonium inhibited the H+ flux by 72% at 50 mM, and the H+ flux could be accelerated two- to threefold by limited proteolysis of intact cells using kallikrein or papain. In cells pretreated with barium, the K(+)-induced H+ flux caused no change of bis-oxonol fluorescence, suggesting an electroneutral pathway. The H+ flux was a saturable function of extracellular K+ (Michaelis constant 55 mM), and flux reversed when the K+ gradient was reversed. Similarly, the H+ flux was a linear function of the H+ gradient and reversed when the H+ gradient reversed. Evidence for ongoing K(+)-induced H+ flux was also found in nonacidified cells. First, changing perfusate K+ from 5 to 50 mM alkalinized baseline cell pH, an effect not reproduced by barium despite an equivalent depolarizing effect. Second, increasing perfusate K+ from 5 to 50 mM completely eliminated the acidification produced by 1 mM amiloride. We conclude that the OK cell expresses two Na(+)-independent acid-base transport systems. One is a barium-sensitive electrogenic H+ conductance and the other functions as an electroneutral K+/H+ antiporter. The antiporter is capable of H+ extrusion from acid-loaded cells but in normal cells functions in the reverse direction, as an H+ loader. The K+/H+ antiporter appears to be one of the major systems regulation cell pH in these cells, balancing the H+ efflux mediated by Na+/H+ exchange.

Acids↗
PubMed1992

Preparative anion-exchange chromatography of soybean trypsin inhibitor: the alternative of column-overload methods.

The objective of preparative separation is to purify the largest amount of material in the shortest time and at a minimum cost, i.e. to maximize throughout. One of the techniques for increasing throughput is to overload the column while maintaining purity and cycle time at the same level. This principle is applied in sample displacement mode chromatography, in which the column is overloaded with sample mixture until it is completely saturated. Soybean trypsin inhibitor was purified from a crude protein extract by this technique using an analytical anion-exchange column with small particle size (20 microns). The comparison of these results, using the criterion of throughput, with those derived from a conventional scale-up, using a 40-microns preparative column, led to the conclusion that the overloaded 20 microns column gave a higher throughput than the 40-microns column.

Anions↗
PubMed1992

Electrogenic Na-independent HCO3 transport in OK cells.

We have shown previously that OK cells recover from an acid load in a medium nominally CO2-free by extruding H via a Na/H exchanger and a passive H-conductive pathway. In this work, the regulation of cell pH (pHi) was studied after addition or withdrawal of CO2/HCO3 (5% CO2, 95 mM HCO3, pH = 8) using the fluoroprobe BCECF. In the presence of Na and amiloride to inhibit Na/H exchange, the recovery of pHi after CO2 entry and CO2 exit were found to depend in part on HCO3 entry and exit, respectively. Efflux of H per se also contributed to restoring pHi after CO2 addition, whereas H influx may have played a smaller role to normalize pHi after CO2 removal. DIDS, 0.5 mM, significantly inhibited both recovery phases of pHi. Removal of Na failed to inhibit the recovery of pHi after CO2 addition and removal. Cl removal also failed to inhibit pHi recovery after CO2 removal. Cell depolarization in the presence of Na moderately stimulated the pHi recovery rate after CO2 addition whereas it markedly inhibited the normalization of pHi after CO2 removal. Cell depolarization in the absence of sodium had only a slight effect to increase pHi recovery after CO2 addition but markedly prevented the pHi recovery after CO2 removal. These results indicate that OK cells lack Na or Cl-dependent HCO3 transport systems. The OK cell possesses a novel stilbene-sensitive electrogenic HCO3 transport system that is involved in the regulation of cell pH.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗