Biomedical subjects

T J Lewis

Publications and source records attributed to T J Lewis.

30 records · Page 2Linked to original sources

PubMed1988

Low-frequency ultrasound absorption in aqueous solutions of hemoglobin, myoglobin, and bovine serum albumin: the role of structure and pH.

New measurements on ultrasound absorption of aqueous solutions of the three globular proteins, bovine hemoglobin, horse heart myoglobin, and bovine serum albumin, at 20 degrees C are reported for the frequency range below 1.2 MHz and, in the case of hemoglobin and bovine serum albumin, to a limited extent for the range 2-30 MHz. The effect of protein conformation has been investigated by use of a range of denaturants and by change of pH. A much more detailed description of protein interactions emerges from the low-frequency studies than was possible hitherto. Specific absorption processes for myoglobin and bovine serum albumin peak in the neighborhood of pH 4.2. The process for myoglobin has a relaxation frequency between 1 and 2.6 MHz, while for bovine serum albumin the frequency is as low as 70 kHz. Both processes can be related to conformational changes in the molecules. In the case of hemoglobin, an absorption process with a relaxation frequency of 600 kHz is found that can be attributed to the dissociation equilibrium of the quaternary structure of the molecule and can be considerably enhanced by denaturants or pH change from neutral to acid conditions. Measurements at frequencies down to 200 kHz have also permitted a more thorough investigation of proton-transfer reactions at carboxyl and amino groups in these proteins and of the effect of pH on these reactions.

Absorption↗

PubMed1987

Electrochemical characteristics of platinum electrodes coated with cytochrome b5-phospholipid monolayers.

Platinum electrodes can be coated with cytochrome b5-phospholipid monolayers by the Langmuir-Blodgett technique. Cyclic voltammetry of a series of dyes shows that the coated electrodes become selective for certain electroactive species. The electron transfer reactions of negatively charged species are inhibited at the modified electrode, whereas positively charged species show enhanced reactivity compared with that at a bare metal electrode.

Animals↗

PubMed1986

Ultrasonic absorption of bovine serum albumin solutions in the frequency range 60 to 160 kHz.

The ultrasonic absorption of the globular protein bovine serum albumin in aqueous solution has been measured in the frequency range 60 to 160 kHz using a 2-1 spherical resonator. The effect of pH change and of the denaturants urea, guanidine hydrochloride, and sodium dodecyl sulfate on the absorption loss has been studied. It is concluded that a significant ultrasonic absorption process exists which is related to structural helix-coil transition equilibria. For native protein the maximum loss appears to occur at a frequency at least as low as 70 kHz for a pH of about 4.2. This loss process is distinct from those arising from proton-transfer equilibria perturbations which are manifest at pH 3.2 and 11.6 and at peak frequencies of 400 kHz and above.

Animals↗

PubMed1985

Ultrasonic absorption of bovine serum albumin solutions in the frequency range 200 kHz-1 MHz.

The ultrasonic absorption of solutions of two electrolytes, magnesium and manganous sulfates, and also of the globular protein bovine serum albumin, has been measured using small volume spherical resonators at frequencies in the range 200 kHz-1.2 MHz. The principles of the technique are discussed and absorption values obtained for the electrolyte solutions at 20 degrees C are compared with existing values using other methods. For BSA, measurements were made at 8 degrees C over a range of pH values. Under both acid and alkaline conditions, excess losses at megahertz frequencies were found to persist down to at least 200 kHz. A new loss peak at approximately 400 kHz has been found at pH 3.2.

Absorption↗

PubMed1982

Electronic processes in biology. The seventeenth Douglas Lea Lecture.

The growing similarities between modern microelectronic circuits and living systems increasingly suggest the electronic nature of the latter. Indeed, the ideas of quantum-mechanical electron tunneling or hopping between localised states developed in physics to explain conduction in non-crystalline solids are readily applicable to biology. Electron tunnelling transitions between energy states localised in biomolecules can explain such vital processes as photosynthesis, respiration and visual reception, and also form a logical framework to explain reactions induced by high energy radiolysis. It is suggested that there is sufficient evidence to support an argument that the same quantum-mechanical tunnelling process will occur through the localised states set up in biopolymers such as the proteins. The consequence would be highly vectorial electron transport along biopolymer pathways, the results of which are shown to have far-reaching implications. There is considerable difficulty in verifying these ideas experimentally and progress has been slow, but it is very probable that electronic physics is now poised to provide a framework for a new understanding of biology.

Biological Transport↗

PubMed1979

Community participation in the certificate-of-need process: a look at ten-taxpayer groups in Massachusetts.

Certificate-of-need statutes give designated state agencies veto power over investment in health care facilities. Some states have sought to temper the arbitrary character of this power by expanding the opportunities for community input into the certificate-of-need process. Massachusetts, for example, has enacted a statute that allows groups of ten taxpayers to petition for a public hearing on any certificate-of-need application. Some observers question whether the benefits of taxpayer-group participation are substantial enough to compensate for the delays and abuses that the statute allegedly invites. To help resolve this question, this Comment examines historical data on Massachusetts taxpayer groups and on their activities and assesses the significance of their composition and tactics to the certificate-of-need process. Although flaws exist in the Massachusetts ten-taxpayer mechanism, in this writer's view it has succeeded partially in making the certificate-of-need process responsive to community opinion. Many groups lack the skills and qualities needed to make constructive use of the ten-taxpayer mechanism. Nevertheless, it serves a valuable purpose by creating a public forum for and by encouraging public participation in the certificate-of-need process, especially by those who might otherwise try to circumvent that process through use of special legislation, of private pressure, or of other similar means.

Certificate of Need↗

PubMed1978

The mechanisms of conduction in proteins.

Theoretical calculations have already shown that the electronic properties of biopolymers may be described in terms of conduction and valence energy bands in which electrons are delocalized to a significant degree. Because these bands are separated by a large energy gap, it is concluded that electronic conduction in such systems must be by 'holes' in the valence band. The mechanism of this conduction is discussed with special reference to dry proteins where the charge-transfer role of appropriate acceptor molecules and the modulating influence of amino acid residues will encourage localized and delocalized hole production at the valence band edge. It is suggested that there are close similarities, which have shown up in measurements, in the electrical behaviour of proteins and other non-biological semi-crystalline solids. The significance of such long-range conduction and attendant polarization is considered briefly in the light of evidence for the existence of proteins in cell membranes and in the skeleton of the cytoplasm

Electric Conductivity↗

PubMed1978

Electronic properties of some protein--methylglyoxal complexes.

Steady-state conductivity measurements and dielectric measurements in the frequency range 10(-5) to 100 Hz are reported for samples of bovine serum albumin, casein, and lysozyme complexed with methylglyoxal. Compared with the untreated proteins, the brown complexed proteins exhibit an increased conductivity and free electron spin density, together with a low-frequency dielectric dispersion. These results can be taken as evidence that the interaction with methylglyoxal results in the proteins possessing an increased electronic activity associated with the creation of mobile electron holes within the valence band states of the protein molecules.

Aldehydes↗

PubMed1974