PubMed Health⌕ Search

Biomedical subjects

R Kilkson

Publications and source records attributed to R Kilkson.

11 recordsLinked to original sources
PubMed1978

Interpretation of light scattering associated with prolonged neural activity and temperature changes.

Changes in light scattering from lobster giant axon which accompany the action potential were observed during periods of prolonged stimulation and as a function of temperature. At an initial temperature of 10 degrees C most (more than 90%) axons produced positive light scattering signals which increased in amplitude when the temperature was lowered. At 2 and 5 degrees C approximately half of the axons produced positive scattering signals. The remaining half produced negative scattering signals which became positive when the temperature was raised to 10 degrees C. The amplitude of the negative signals followed sigmoid transition to positive values as a function of time. The time and temperature dependence of the signal are interpreted in terms of differential changes between the indices of refraction of the membrane matrix and the open or closed early activation channel.

Action Potentials↗
PubMed1977

Light scattering and excitation in lobster giant axon. Effects of ion substitution.

Changes in the light scattering signal from single giant axons of lobster were observed during the propagation of the action potential in order to correlate membrane excitability with possible structural changes reflected in the optical properties of the axolemma. Substitution of guanidine and aminoguanidine for sodium resulted in a decreased action potential amplitude to 69 and 50% of control values, respectively. The amplitude of the light signal was, however, not significantly changed by these substitutions and is, therefore, reported to be independent of the transmembrane potential and current. The venom of the scorpion Leiurus quinquestriatus caused a marked prolongation of the action potential and the light scattering signal without significantly altering their amplitudes. A two-state model of the early (sodium) activation channel is suggested, in which the light scattering signal is correlated with a possible difference in the scattering efficiency between the states of the channel.

Action Potentials↗
PubMed1976

Application of polarization effects in light scattering: a new biophysical tool.

We demonstrate that a newly developed instrument which measures all polarization and intensity information contained in differentially and elastically scattered light has valuable applications in biology. The polarization states of light scattered differentially from suspensions of biological scatters are shown to contain structural information about those systems. The scatterers are discussed in the context of a 16 component matrix which completely characterizes the scattering process. The instrument and method are described in terms of the corresponding matrix algebra. We also discuss the use of the instrument as a device for distinguishing between closely related structural systems and as a tool for following time-dependent structural changes.

Bacillus subtilis↗
PubMed1975

Intrinsic asymmetry of oligomer transitions and biomolecular evolution.

Structural transitions in oligomeric proteins due to ligand binding are important in biomolecular regulatory processes. The transitions may occur on the secondary, tertiary or quarternary structure levels. Detailed consideration of the time sequence of ligand binding to the oligomer shows that there is an intrinsic dynamic asymmetry in all oligomer transitions, even if the initial and the final state are completely symmetric. This asymmetry has important bearing on the evolution and the divergence of the primary structure (amino acid sequence) of oligomeric proteins. It may explain (at least in part) the occurrence of oligomeric proteins with similar but not identical protomers. Certain specific groups of oligomers are shown to be under greater evolutionary pressure for protomer structure divergence. The dynamic asymmetry of oligomer transitions also results in higher complexity in reaction kinetics. Some implications on ribosome structural evolution are discussed.

Biological Evolution↗
PubMed1965

Inactivation of oriented bacteria with polarized ultraviolet light.

Aligned deoxyribonucleic acid (DNA) molecules exhibit a large absorption anisotropy in the ultraviolet (UV) region of the spectrum (11). Also, the UV action spectra of most bacteria resemble the absorption spectrum of DNA (23), implying that inactivation is directly proportional to the UV absorbed by the bacterial DNA. Hence, the UV sensitivity of aligned uniaxial bacteria might be anisotropic with respect to polarization of the incident UV (17, 19). Any inactivation anisotropy would depend upon the orientation of DNA within the bacteria, as well as upon the alignment of bacteria, and could provide a more sensitive indication of in vivo DNA orientation than is presently available using optical methods (5, 12-16). Using an electric field of 3.5 x 10(6) cycles/second, samples of bacteria of strain LS-301 were aligned in a quartz cell and were irradiated with UV (lambda = 2652 A) polarized perpendicular and parallel to the alignment direction. The resultant survival curves resolved no inactivation anisotropy. This result is interpreted to mean that there was insufficient bacterial DNA alignment to give a detectable anisotropy. The minimum average DNA alignment necessary to have resolved an anisotropy is calculated to be 15 per cent in an axial direction (bases perpendicular to the bacterial axis) or 30 per cent in a radial direction (bases parallel to the bacterial axis).

Bacteria↗