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At least 343 records · Page 19Linked to original sources
PubMed1998

DNA bound to polypyrrole films: high-resolution imaging, DNA binding kinetics and internal migration.

We have studied the time-dependent uptake of 35S radiolabeled DNA with electrochemically prepared polypyrrole films. The two distinct polypyrrole film surfaces, a rough (solution polymeric growth face, R) and a smooth surface (electrode face, S) were characterized by low-resolution AFM and high-resolution transmission electron microscopy (TEM). These studies showed the presence of steep contours and defects in the form of large and small surface holes and valleys on the rough surface of polypyrrole. The void dimensions ranged from the nanoscale to micron size. By contrast, the smooth surface was flatter and largely devoid of significant structural defects and exhibited closer packing of the polypyrrole chains over large areas. Both surfaces were comprised largely of chains whose average diameters were 1.0-1.2 +/- 0.3 nm. The surface characterization studies were complemented by time-dependent DNA uptake studies which showed a t1/2-dependent total uptake of 35S DNA at higher levels on the rough surface compared to the smooth surface. This is consistent with the apparent higher effective surface area of the rough surface compared to the smooth. Using a proportional counter the time-dependent ratio (R/S) of the 35S DNA detected from the rough surface of the polypyrrole disk to that detected from the smooth surface suggested that DNA was migrating into the disk interior from its uptake surface. The rough side defect dimensions measured by TEM were more than sufficient to allow for the penetration and migration of DNA into the disk interior. Both R/S ratios were extrapolated and found to intersect at an R/S value close to 1.0, suggesting a kinetic process leading ultimately towards a nearly uniform radiolabeled DNA distribution in the disk. These kinetic results were in agreement with the surface characterization studies and suggest a model in which sizeable internal pores exist throughout the electrochemically prepared polypyrrole, that could account for the DNA migration effect. This was confirmed by TEM of the interior of a polypyrrole disk produced by Argon ion milling.

Adsorption↗
PubMed1993

Perturbations of the distal heme pocket in human myoglobin mutants probed by infrared spectroscopy of bound CO: correlation with ligand binding kinetics.

The infrared spectra of CO bound to human myoglobin and myoglobin mutants at positions His-64, Val-68, Asp-60, and Lys-45 on the distal side have been measured between 100 and 300 K. Large differences are observed with mutations at His-64 and Val-68 as well as with temperature and pH. Although distal His-64 is found to affect CO bonding, Val-68 also plays a major role. The variations are analyzed qualitatively in terms of a simple model involving steric interaction between the bound CO and the distal residues. A strong correlation is found between the final barrier height to CO recombination and the CO stretch frequency: as compared to wild type, the barrier is smaller in those mutants that have a higher CO stretch frequency (vCO) and vice versa. Possible reasons for this correlation are discussed. It is emphasized that the temperature and pH dependence of both the kinetics and the infrared spectra must be measured to obtain a consistent picture.

Carbon Monoxide↗
PubMed1984

Apical membrane properties and amiloride binding kinetics of the human descending colon.

The apical membrane properties of the isolated human descending colon were characterized by use of current fluctuation analysis methods and microelectrode techniques. The Na+ channel blocker amiloride was used to evaluate apical membrane conductance and the transepithelial short-circuit current (Isc). Amiloride significantly reduced Isc and increased the membrane resistance ratio. At submaximal doses of amiloride in the mucosal bathing solution, fluctuation analysis of the Isc revealed a Lorentzian component in the power-density spectra. The dose-response relationship between amiloride and current noise parameters was consistent with a two-state mechanism of blocker interaction with the channel. The on and off rate constants for the blocker-receptor reactions, the single-channel currents, and the Na+ channel density were estimated and were similar to those from Na+ channels from other so-called tight epithelia. In addition, these studies revealed an amiloride-insensitive conductance in the apical membrane in parallel to the amiloride-blockable Na+ channels. This conductance may be due to potassium ions. If so, the apical membrane properties of the human descending colon may closely resemble those of the rabbit descending colon and rat distal colon.

Adult↗
PubMed2000

T cell receptor binding kinetics and special role of Valpha in T cell development and activation.

The kinetics of the interaction between T cell receptor (TCR) and major histocompatibility complex (MHC) has an important role in determining thymocyte-positive and -negative selection in the thymus, as well as in T cell activation. The alpha chain of the TCR is the major player in determining how the TCR fits onto the MHC ligand, and thus has a major role in determining whether a T cell develops as class I or class II restricted. In this article, we summarize recent data from our laboratory and others on the role of polymorphism in the Valpha combining site in determining MHC class restriction, and on kinetic parameters in thymocyte selection.

Animals↗
PubMed1990

Physicochemical and enzyme binding kinetic properties of a new angiotensin-converting enzyme inhibitor ramipril and their clinical implications.

After oral administration, ramipril, a nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor, is transformed in the liver into its active metabolite ramiprilat. Because of its pentane ring it is at least 23 times more lipophilic than enalaprilat. The in vitro affinity for ACE is 7 times higher than for enalaprilat and 47 times higher than for captopril. The ramiprilat-ACE complex is therefore very stable and dissociates 6 times more slowly than the enalaprilat ACE complex and 72 times more slowly than the captopril ACE complex. Consequently, ramipril is pharmacologically more potent and has a longer duration of action than enalapril and captopril. The blood pressure lowering effect of ACE inhibitors is attributed to the decrease in angiotensin II in serum and locally in target organs of hypertension: heart, vessel wall, kidney and brain. Inhibition of tissue renin-angiotensin system by ramipril has been described in target organs of hypertension in animal models and in clinical studies. Possibly due to its high lipophilicity, and strong affinity to the converting enzyme a better tissue penetration and a more pronounced local ACE inhibition in the target organs has been observed, as compared to other ACE inhibitors. In a preliminary investigation a direct action of ramipril on the tissue RAS in hypertensive patients could also be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1986

Interrelations between anti-tumour activity, DNA breakage, and DNA binding kinetics for 9-aminoacridinecarboxamide anti-tumour agents.

For a series of 9-aminoacridinecarboxamides, anti-tumour activity in vivo and cytotoxicity in vitro are correlated directly with the ability of the compounds to cause DNA single-strand breaks and with their DNA-dissociation mechanisms and residence times. It is suggested that one important consequence of long DNA residence times may be an enhanced ability to cause DNA strand breaks by a non-oxidative mechanism.

Aminoacridines↗
PubMed1979

Scintillation-proximity assay of antigen-antibody binding kinetics: concise communication.

Tritiated latex particles and scintillant latex particles have been covalently coated with an antigen (human albumin) and both types of particles are than combined in dilute aqueous suspensions. The formation of antibody-induced dimer and higher-order aggregation resulted in scintillations that could be measured in a standard liquid-scintillation counter, energy-gated for H-3. Rabbit anti-human antiserum was easily detected at a titer of 1:10(6). Human albumin, in the inhibition mode, was also easily detected at 0.1 ng/ml. Since the samples are nondestructively assased, it was possible to examine the kinetics of aggregation under a variety of conditions.

Albumins↗