Search PubMed⌕ Search

Biomedical subjects

S Bone

Publications and source records attributed to S Bone.

At least 19 recordsLinked to original sources
PubMed2004

The interaction of trypsin with trehalose: an investigation of protein preservation mechanisms.

Preservation of the native protein structure and biological activity in dry protein/excipient mixtures has been previously attributed to either the glass forming properties of the additives or to their ability to hydrogen bond to the protein. There is evidence that both processes are important but it has not yet been elucidated which is the limiting factor that determines the efficiency of a given molecule as a protectant. In this work, gravimetric measurements together with enzyme activity assays have been employed to investigate the protection of proteins by sugars, through direct interaction via hydrogen bonding and as the result of glass formation. As a model protein, trypsin has been employed and the modes of action of two similar disaccharides, sucrose and trehalose, which offer different levels of protection, evaluated and compared. Data obtained on freeze-dried formulations indicate that protein and sugars interact through hydrogen bonding to protein hydration sites. The extent of interaction is found to change dramatically at elevated temperatures; sucrose showing a significantly decreased, and trehalose a considerably increased level of interaction. Protein preservation is shown to be directly related to the number of hydrogen bonds formed. Possible reasons why trehalose interacts more extensively with the protein than sucrose are discussed in terms of differences in the anhydrous structures and molecular mobilities of the sugar molecules.

Protein Binding↗
PubMed2001

Characterisation and optimisation of AC conductimetric biosensors.

Urease, immobilised on interdigitated gold electrodes, is employed as a model enzyme for characterisation and optimisation of a.c. conductimetric sensors. The sensors' response is measured over a frequency range of 20 Hz to 300 kHz and an optimum operating frequency established. The activity of the urease, both in solution and immobilised states, is investigated and Km values obtained. The effect of method of immobilisation and enzyme loading on the sensors' performance are studied and urease electrodes are characterised as a function of temperature, pH and electrolyte concentration. An important finding, particularly for conductimetric sensors designed for clinical use, is that proper consideration of the effects of electrode polarisation must be taken into account in order to maintain high sensor sensitivity at physiological electrolyte concentrations. Measurements of urea concentration in untreated serum are described.

Biosensing Techniques↗
PubMed2000

An investigation of the water-binding properties of protein + sugar systems.

The water-binding properties of sucrose + beta-lactoglobulin and trehalose + beta-lactoglobulin prepared by freeze-drying, spray-drying and evaporation from solution have been studied using gravimetric methods. The hydration characteristics of the individual sugars are dependent on the method of drying, and different isotherms have been recorded for each of the sample preparations. However, the initial hydration isotherms produced for the sugar + protein samples appear to be very similar for each sample type irrespective of drying method, with the sugar present in the amorphous glassy form in all cases. There is evidence of interaction between the sugar in this form and protein, specifically in the hydration region where single hydrogen-bonded water is expected to be bound. The magnitude of the interaction appears to be of the same order for both sugars. Irrespective of the method of preparation, rehydration of the sugar + protein complexes above a critical value causes a transition resulting in the sugar adopting a crystalline form and phase separation of the sugar and protein. In this crystalline form there is no evidence of interaction between the sugar and protein. For sugar + protein samples prepared by evaporation from solution, a small amount (approximately 3% by weight) of water is trapped in the complex even under extreme conditions of dehydration.

Animals↗
PubMed1998

Dielectric studies of chain melting and denaturation in native DNA.

Dielectric methods, based on time domain reflectometry (TDR), have been employed to characterise DNA chain melting and denaturation. A dielectric dispersion has been identified, centred in the low megahertz region, which has been attributed to the fluctuation of counterions along short segments of the DNA chain. Chain melting studies have shown that the magnitude of this dispersion is dependent not only on the relative proportions of single to double stranded DNA but also on the intermolecular interactions between the DNA chains.

Animals↗
PubMed1996

Dielectric studies of intermolecular interactions in native DNA.

The concentration dependence of the high frequency dielectric dispersion exhibited by solutions of DNA and the sensitivity of this to the ionic strength of the solution are described. Dielectric data obtained are consistent with a model involving the fluctuation of counterions along short segments of the DNA chain. The concentration and ion strength dependencies are discussed in terms of intermolecular interactions which are considered responsible for the existence of structure in DNA solutions.

Animals↗
PubMed1996

Time-domain reflectometry studies on Halobacterium halobium and Halobacterium marismortui.

The dielectric properties of Halobacterium halobium and Halobacterium marismortui measured over the frequency range 1 MHz to 1 GHz are compared with a single-shell model for interfacial polarization. In the case of Halobacterium halobium, the model shows excellent agreement with the experimental data for reasonable values of membrane and cytoplasmic conductivity and permittivity. For Halobacterium marismortui however, an acceptable fit to the data can only be achieved by invoking a plasma membrane conductivity some three orders of magnitude larger than that of Halobacterium halobium and adding a second high-frequency dielectric dispersion. These observations confirm the findings of a previous study and are consistent with a scheme for Halobacterium marismortui involving thermodynamic compartmentalization of Na and K ions and the existence of a conductive plasma membrane.

Cell Membrane↗
PubMed1996

Dielectric and gravimetric studies of water binding to lysozyme.

Time domain dielectric spectroscopy and hydration isotherm measurements as a function of temperature have been applied to hydrated lysozyme powder. Two dielectric dispersions were identified, the first centred at approximately 8 MHz and a second above 1 GHz. The higher dispersion is considered to be the result of rotational relaxation of water molecules bound to the enzyme. In this case the results indicate the existence of a population of 32 water molecules per lysozyme molecule which are irrotationally bound to the lysozyme structure. A larger population of water molecules is relatively free to respond to the electric field and exhibits a dipole moment close to that of vapour phase water molecules. Multi-temperature hydration isotherm measurements are used to calculate enthalpies and entropies associated with the binding of water to lysozyme. Discontinuities both in dielectric and in thermodynamic characteristics in the range 10-14% hydration are interpreted as a re-ordering of the water structure on the enzyme surface.

Animals↗
PubMed1995

Dielectric studies of ion fluctuation and chain bending in native DNA.

The high-frequency dielectric dispersion exhibited by solutions of native DNA is characterised as a function of electrolyte concentration, counterion type, temperature and pH. The data are interpreted in terms of counterion fluctuation along short segments (subunits) of the DNA chain. From calculation of the subunit length from dielectric relaxation time and increment, information is derived regarding the static and dynamic bending of the DNA chain. Activation enthalpies for the ion fluctuation process are obtained from temperature-dependent dielectric data.

Animals↗
PubMed1994

Dielectric studies of native, unfolded and intermediate forms of beta-lactamase.

Time-domain dielectric spectroscopy has been applied to native, intermediate and unfolded beta -lactamase structures both in the hydrated solid state and in solution. Gravimetric and dielectric measurements indicate that nearly three times as many water molecules are multiply hydrogen bonded to the unfolded compared with the native protein. By contrast, the primary hydration population of the state A intermediate is only 20% larger than that of the folded enzyme. Analysis of the beta -dispersions in terms of rotational relaxation of the protein's permanent dipole has indicated that there is no significant difference in the dimensions of the three structures. This is not consistent with the findings of previous studies employing different experimental techniques.

Models, Chemical↗
PubMed1993

Time-domain dielectric spectroscopy applied to cell suspensions.

A precision difference time-domain reflectometry (TDR) technique is described for the investigation of the dielectric properties of cell suspensions. The dielectric spectra obtained for erythrocytes using TDR are comparable with those reported in previous dielectric studies employing frequency-domain technique.

Animals↗
PubMed1991

Proton pathways in lysozyme.

Protonic conduction studies are reported for lysozyme as a function of the number of bound water molecules. Lysozyme samples employing proton-injecting palladium black electrodes exhibited conductivities up to eight orders of magnitude greater than those retained between control (copper) electrodes. The results indicate that water involved in multiple hydrogen bond contact with the enzyme together with hydrogen bonded segments of the enzyme structure provide a hydrogen bond network which is capable of supporting considerable protonic conduction.

Copper↗
PubMed1989

Uterine positions and schedules of urination: correlates of differential maternal anogenital stimulation.

Lactating Mongolian gerbils, like lactating Norway rats, reliably lick some pups in their litters more than they lick others. Male gerbil pups are licked more by their dams than are their sisters and some males and some females within each litter are licked more often than are their sibs of the same sex. In the present article, we explore the characteristics of same-sex littermates that are correlated with elicitation of extreme amounts of maternal anogenital licking. We found that both the male pup and the female pup in a litter of gerbils that received the most maternal anogenital licking: (1) released greater quantities of urine and (2) exhibited longer latencies to begin to urinate in response to artificial anogenital stimulation than did the male pup and the female pup in a litter that received the least amount of maternal anogenital licking. We also found that foster mothers rearing Caesarean-delivered litters spent more time licking the anogenital areas of: (1) those male pups that, as fetuses, had occupied uterine locations adjacent to relatively few females and (2) those female pups that, as fetuses, had occupied uterine locations adjacent to relatively many males. We discuss implications of these findings for understanding of how maternal behavior may mediate hormonal effects on the development of young gerbils.

Animals↗
PubMed1988

Time domain reflectrometry: the difference method applied to conductive aqueous solutions.

The precision difference time domain reflectrometry method has been developed for application to conductive aqueous solutions. The sensitivity of the technique has been investigated with protein and polypeptide solutions over the frequency range 100 kHz to 1 GHz. Loss processes with an absorption maximum of 0.3 have been successfully measured and larger dispersions characterised in KCl concentrations as high as 100 mM.

Electric Conductivity↗
PubMed1987

Time-domain reflectrometry studies of water binding and structural flexibility in chymotrypsin.

Time-domain dielectric spectroscopy has been employed to probe the hydration properties and structural flexibility of chymotrypsin (EC 3.4.21.1). The dielectric properties of the hydrated protein above 100 MHz have been used to identify two categories of protein-bound water, the first being irrotationally bound to the protein with a second, relatively weakly bound, having a rotational freedom comparable with that of normal bulk water. A dielectric dispersion observed, centred at 12 MHz, has been attributed to the relaxation of the polar components of the protein structure. This dielectric loss became increasingly significant above a transition in the hydration dependence, where water is relatively weakly bound to the chymotrypsin. This is discussed in terms of the formation of water clusters on the protein surface which screen electrostatic interactions between protein-charged groups.

Chemical Phenomena↗
PubMed1985

Dielectric studies of protein hydration and hydration-induced flexibility.

Dielectric measurements, as a function of hydration, are reported for collagen, cytochrome-c, elastin and lysozyme powders. The hydration dependence of the dispersion that occurs in the frequency range between 10 kHz and 10 GHz has been used to identify two classes of protein-bound water molecules (namely, rotationally hindered or unhindered), as well as the hydration level for the onset of an increasing protein flexibility. Such studies can aid an understanding of the relationship between enzyme activity and structural flexibility, and of hydration-induced changes in the structure and dynamics of protein structures.

Collagen↗