Effect of glutaraldehyde on the activity of some DNA restriction endonucleases

The effect of the bifunctional crosslinking reagent glutaraldehyde on the activity of the restriction enzymes Bam HI,Hind III, EcoRI, and Tthlll I was investigated. The four enzymes exhibited differential sensitivity to inactivation. Tthlll I was the most sensitive, with activity losses occurring at levels of 0.0025% and above.Hind III was the most stable of the four and remained fully active at concentrations as high as 0.075%. Addition of BSA to incubation mixtures generally had a stabilizing effect. Implications of these results for the design of glutaraldehyde-based methods for the immobilization of restriction endonucleases are discussed.     

Structural changes of the gold-support interface during CO oxidation catalyzed by mononuclear gold complexes bonded to zeolite NaY: evidence from time-resolved X-ray absorption spectroscopy

Mononuclear gold complexes synthesized from AuIII(CH3)2(acac) in zeolite NaY were characterized by time-resolved X-ray absorption spectroscopy and infrared spectroscopy as they catalyzed CO oxidation at 298 K and 760 Torr in flow systems. Initial contact with a CO + O2 mixture led to the rapid formation of cationic gold complexes in which Au was bonded to approximately two zeolite O atoms, on average. Further contact with CO + O2 led to breaking of an Au-surface oxygen bond, giving a gold carbonyl anchored to approximately one O atom. The process was reversed in the absence of CO and O2.     

Small Heteroborane Cluster Systems. 6. Mössbauer Effect Study of Iron Substituted Small Metallaborane Clusters

The M?ssbauer effect spectra for a series of small [Fe(eta(5)-C(5)H(5))(CO)(x)()] substituted metallaborane complexes are reported, where x = 1 or 2. The pentaborane cage in compounds [Fe(eta(5)-C(5)H(5))(CO)(2)B(5)H(7)P(C(6)H(5))(2)] (1), [Fe(eta(5)-C(5)H(5))(CO)(2)B(5)H(8)] (2), and [(Fe(eta(5)-C(5)H(5))(CO)(2))(2)B(5)H(7)] (3) was found to act as a significantly better donor ligand than the ligands in a comparison group of previously reported [Fe(eta(5)-C(5)H(5))(CO)LX] complexes, where L = CO or PPh(3) and X = halide, pseudohalide, or alkyl ligands. These metallaborane complexes were found to most resemble their silyl analogues in M?ssbauer spectral parameters and the electronic distribution around the iron centers. In addition, the M?ssbauer data showed that the [&mgr;-2,3-(P(C(6)H(5))(2)B(5)H(7)](-) ligand was a superior donor to the corresponding unsubstituted [B(5)H(8)](-) ligand. The M?ssbauer spectral results for the metallaborane complexes studied were found to be in general agreement with the anticipated donor and accepting bonding considerations for the cage ligands based upon their infrared and (11)B NMR spectra and X-ray structural features. The M?ssbauer data for the [Fe(eta(5)-C(5)H(5))(CO)B(4)H(6)(P(C(6)H(5))(2))] (4) and [Fe(eta(5)-C(5)H(5))(CO)B(3)H(7)(P(C(6)H(5))(2))] (5) complexes, in comparison with compound 1, showed that as the borane cage becomes progressively smaller, it becomes a poorer donor ligand. A qualitative relationship was found between the observed M?ssbauer isomer shift data and the number of boron cage vertices for the structurally related [Fe(eta(5)-C(5)H(5))(CO)(x)B(y)H(z)P(C(6)H(5))(2)] complexes, where x = 1 or 2, y = 3-5, and z = 6 or 7. The X-ray crystallographic data for compounds 1, 2, 5, and [Fe(eta(5)-C(5)H(5))(CO)B(5)H(8)] (6) were also found to agree with the trends observed in the M?ssbauer spectra which showed that the s-electron density on the iron nucleus increases in the order 5 < 6 < 2 < 1. The X-ray crystal structure of complex 2 is also reported. Crystallographic data for 2: space group P2(1)/c (No. 14, monoclinic), a = 6.084(3) ?, b = 15.045(8) ?, c = 13.449(7) ?, beta = 99.69(5) degrees, V = 1213(1) ?(3), Z = 4 molecules/cell.     

POLARIZED FLUORESCENCE OF 5-METHYLCYTOSINE SPECIES IN SOLUTION AT ROOM TEMPERATURE

Fluorescence yields (π_f,'s) and polarizations ( P ) are measured for aqueous 5-methylcytosine (˜ 0.1 m M ) at 20°C as a function of pH over the range 2–14. Both properties change abruptly and in parallel at pH's corresponding to the known pK_a values. Polarizations were also obtained for the 5-methylcytosine cation, neutral and anion species in ethylene glycol water glass at ˜180K. The weak fluorescence of the neutral and cation species at 20°C was polarized almost as highly as at low temperature. When the fluorescence lifetimes are assumed to be correctly given by the product of calculated radiative lifetimes and quantum yields, the polarizations are found to be consistent with rotational diffusion rates ˜4 times faster than predicted from Stokes-Einstein models for the neutral and anion species. The cation seemed to rotate about two times more slowly than the neutral and anion species. It was also shown that the properties of the three species are such that a plot of 1/P vs apparent π_f in the pH range 2–11 is fortuitously linear.     

Comprehensive thermodynamic characterization of the metal-hydrogen bond in a series of cobalt-hydride complexes

A detailed structural and thermodynamic study of a series of cobalt-hydride complexes is reported. This includes structural studies of [H(2)Co(dppe)(2)](+), HCo(dppe)(2), [HCo(dppe)(2)(CH(3)CN)](+), and [Co(dppe)(2)(CH(3)CN)](2+), where dppe = bis(diphenylphosphino)ethane. Equilibrium measurements are reported for one hydride- and two proton-transfer reactions. These measurements and the determinations of various electrochemical potentials were used to determine 11 of 12 possible homolytic and heterolytic solution Co-H bond dissociation free energies of [H(2)Co(dppe)(2)](+) and its monohydride derivatives. These values provide a useful framework for understanding observed and potential reactions of these complexes. These reactions include the disproportionation of [HCo(dppe)(2)](+) to form [Co(dppe)(2)](+) and [H(2)Co(dppe)(2)](+), the reaction of [Co(dppe)(2)](+) with H(2), the protonation and deprotonation reactions of the various hydride species, and the relative ability of the hydride complexes to act as hydride donors.     

A coupled two-compartment model for immobilized enzyme electrodes

The effect of stirring on the transient and pseudo steady-state behavior of potentiometric and amperometric immobilized enzyme electrodes is accurately modelled by a coupled two-compartment system of nonlinear differential equations. In the first compartment, the enzyme layer, the chemistry is governed by enzyme kinetics and diffusion. This is coupled to the second compartment, the bulk solution, which is controlled only by molecular diffusion. Several results of analytical significance can be obtained by using this model: for example, it is shown how the stirring rate can be used to increase the linear dynamic range.     

Drying and hydrophobic collapse of paraffin plates

We perform molecular dynamics simulations of the hydrophobic collapse of two paraffin plates to examine how the collapse is mediated by realistic paraffin-water attractive van der Waals forces. We explore several aspects of the drying transition between the plates, including the critical separation for drying and the critical size of the vapor bubble required for the nucleation of the drying event. We also investigate the kinetics of hydrophobic collapse and find that the hydrophobic collapse occurs in about 100 ps. We compare these results with the simulations with the plate-water van der Waals attractions turned off and with recent results on the hydrophobic collapse of multidomain proteins. Last, we discuss the relationship among the dewetting transition critical distance, van der Waals potential well depth, and water contact angle on solute surface using a simple macroscopic theory.     

Rapid computer simulation of ESR spectra. Conventional ESR of axially symmetric 14N-nitroxide spin labels

A computer algorithm is presented for the simulation of the effect of molecular tumbling on ESR spectra, and is applied to simulation of the conventional ESR signal (the absorption signal detected at the first harmonic of the modulation frequency and in-phase with the modulation frequency, in the limit of low microwave and modulation power) of axially symmetric ¹⁴N-nitroxide spin labels. The algorithm is extremely fast and is economical in terms of computer memory requirements.     

Enterococcal cytolysin: a novel two component peptide system that serves as a bacterial defense against eukaryotic and prokaryotic cells

The cytolysin is a novel, two-peptide lytic toxin produced by some strains of Enterococcus faecalis. It is toxic in animal models of enterococcal infection, and associated with acutely terminal outcome in human infection. The cytolysin exerts activity against a broad spectrum of cell types including a wide range of gram positive bacteria, eukaryotic cells such as human, bovine and horse erythrocytes, retinal cells, polymorphonuclear leukocytes, and human intestinal epithelial cells. The cytolysin likely originated as a bacteriocin involved with niche control in the complex microbial ecologies associated with eukaryotic hosts. However, additional anti-eukaryotic activities may have been selected for as enterococci adapted to eukaryotic cell predation in water or soil ecologies. Cytolytic activity requires two unique peptides that possess modifications characteristic of the lantibiotic bacteriocins, and these peptides are broadly similar in size to most cationic eukaryotic defensins. Expression of the cytolysin is tightly controlled by a novel mode of gene regulation in which the smaller peptide signals high-level expression of the cytolysin gene cluster. This complex regulation of cytolysin expression may have evolved to balance defense against eukaryotic predators with stealth.