Biomedical subjects

Jacqueline Keyhani

Publications and source records attributed to Jacqueline Keyhani.

5 recordsLinked to original sources

PubMed2005

Sensitivity to detergents and plasmid curing in Enterococcus faecalis.

This research reports the sensitivity of a clinical isolate of Enterococcus faecalis to sodium N-lauroylsarcosinate (sarkosyl) and sodium dodecyl sulfate (SDS), as well as the efficiency of these detergents in curing the strain. Compared to Escherichia coli, Enterococcus faecalis was very sensitive to both detergents, with minimum inhibitory concentrations (MIC) for the latter being 100 times lower than for Escherichia coli. The clinical isolate of Enterococcus faecalis used in this study exhibited plasmid-borne resistance to kanamycin (MIC 2 mg/ml) and tetracycline (MIC 50 mug/ml); 3% curing was observed after growth in the presence of sarkosyl but no curing was observed after growth in the presence of either SDS or acridine orange. In contrast, 35% curing of plasmid-bearing Escherichia coli was observed after growth in the presence of either SDS or acridine orange, but none was observed after growth in the presence of sarkosyl.

Acridine Orange↗

PubMed2005

Stepwise binding of nickel to horseradish peroxidase and inhibition of the enzymatic activity.

The incubation of horseradish peroxidase C (HRPC) with millimolar concentrations of nickel, at room temperature and at pH 4.0, induced the progressive formation of a metal-enzyme complex characterized by alterations of the enzyme Soret absorption band that were time- as well as nickel concentration- dependent. For any given incubation period between 1 and 60 min, 2 values for the apparent dissociation constant (K(d)) were found, suggesting the presence of binding sites with different affinities for nickel. The value of each K(d) dropped as the incubation time increased, indicating a progressive stabilization of the metal-enzyme complex. Hill plots suggested a cooperative binding of up to four Ni2+ ions per molecule of HRPC. The inhibition of the enzymatic activity by nickel was studied by following the H2O2-mediated oxidation of o-dianisidine by HRPC under steady-state kinetic conditions. Ni2+ was found to be either a noncompetitive or a mixed inhibitor of HRPC depending both on the duration of preincubation with the enzyme and on Ni2+ concentration. The enzyme remained active only over a limited metal concentration range and data indicated that binding of one Ni2+ affected the substrate binding site, binding of a second Ni2+ affected both substrate and peroxide binding sites, and binding of more than 2 Ni2+ per HRPC molecule led to complete loss of enzymatic activity. Results pointed to the damaging effects of prolonged exposure to heavy metals and also to the existence of a critical metal concentration beyond which immediate abolishing of enzymatic activity was observed.

Catalysis↗

PubMed2004

Plasma membrane alteration is an early signaling event in doxorubicin-induced apoptosis in the yeast Candida utilis.

Signaling pathways such as increased ceramide, mitochondrial dysfunction, and P3 and caspase activation are produced by anticancer drugs and lead to apoptosis. In this research we show that the first event after culturing the yeast Candida utilis in the presence of low doses of doxorubicin (25 microg/mL) is the morphological alteration of the plasma membrane. In the presence of higher doxorubicin doses (>/=50 microg/mL), in addition to profound alterations in the plasma membrane, changes in mitochondrial shape and cristae organization were observed. Concomitantly, increases in respiration, substrate oxidation, and cytochrome biosynthesis were observed at low doxorubicin doses (up to 25 microg/mL), whereas a progressive decrease was observed at higher doses. [(3)H]Leu incorporation into proteins increased by 40% in the mitochondrial fraction and by 19% in the cytosol in the presence of 25 microg/mL doxorubicin; it decreased to 80% of the control in the cytosol in the presence of 1 mg/mL doxorubicin. Morphologically, doxorubicin doses of up to 200 microg/mL produced apoptosis, whereas higher doxorubicin doses produced necrosis.

Apoptosis↗

PubMed2004

Hypoxia/anoxia as signaling for increased alcohol dehydrogenase activity in saffron (Crocus sativus L.) corm.

Alcohol dehydrogenase, NAD-dependent lactate dehydrogenase, and NAD-independent lactate dehydrogenase activities were investigated in corms cultivated in normoxic and hypoxic/anoxic conditions. Depending on the developmental stage, hypoxia/anoxia was a signal for increase in either alcohol dehydrogenase or NAD-dependent lactate dehydrogenase. NAD-independent lactate dehydrogenase contributed to the recycling of lactate, thus preventing acidosis.

Alcohol Dehydrogenase↗

PubMed2003

Heterogeneous inhibition of horseradish peroxidase activity by cadmium.

Inhibition of horseradish peroxidase (HRP) activity by cadmium was studied under steady-state kinetic conditions after preincubation of the enzyme with millimolar concentrations of Cd(2+) for various periods of time. The H(2)O(2)-mediated oxidation of o-dianisidine by HRP was used to assess the enzymatic activity. Cd(2+) was found to be either a noncompetitive inhibitor of HRP or a mixed inhibitor of HRP depending both on the duration of incubation with HRP and on Cd(2+) concentration. Furthermore, for the same inhibition type, K(i) values dropped as incubation time increased. These results suggested that Cd(2+) would slowly bind to the enzyme and progressively induce conformational changes. Spectrophotometric analysis showed that indeed Cd(2+) altered the heme Soret absorption band on binding HRP and exhibited a K(d) which decreased as the incubation time of HRP with Cd(2+) increased. Hill plots suggested a cooperative binding of up to three Cd(2+) ions per molecule of HRP. Thus, Cd(2+) binding to HRP resulted in progressive inhibition of enzymatic activity with a change in the inhibition type as the number of Cd(2+) ions per HRP molecule increased. Results also illustrated the potential danger of long-term exposure to heavy metals, even for enzymes with low affinity for them.

Binding Sites↗