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Biomedical subjects

A Katchalsky

Publications and source records attributed to A Katchalsky.

At least 19 recordsLinked to original sources
PubMed1973

An attempt at an integral interpretation of nerve excitability.

A qualitatively consistent integral interpretation of biochemical, electrophysiological, and biophysical data on nerve activity is given in terms of a basic excitation unit. This operational term models a dynamically coupled assembly of membrane components accounting for graded and all-or-none responses upon stimulation. The analysis contains a series of suggestions linking controversial interpretations and is aimed at stimulation of experimental studies providing the basis for a quantitative integral theory of nerve excitation.

Acetylcholine↗
PubMed1972

Hysteresis and conformational changes in ribosomal ribonucleic acid.

Both rat liver and Escherichia coli rRNA in 0.1m-sodium chloride were titrated with acid or alkali over the range pH3-7 at approx. 0 degrees C. rRNA did not bind acid reversibly and hysteresis was observed, i.e. the plot of acid bound to rRNA against pH had the form of a loop showing that the amount of acid bound at a particular pH depended on the direction of the titration. Although the boundary curves were reproducibly followed on titration from pH7 to 3 and from pH3 to 7, points within the loop were ;scanned', e.g. by titration from pH7 to a point in the range pH3-4 followed by titration with alkali to pH7. It is inferred that the ;lag' in the release of certain bound protons is at least 1 pH unit, that at least about 9-15% of the titratable groups (adenine and cytosine residues) that are involved in this process and that the free energy dissipated in completing a cycle is approx. 4.2kJ/mol (1kcal/mol) of nucleotide involved in hysteresis. The interpretation of the ;scanning' curves was illustrated by means of a cycle of possible changes in the conformation of a hypothetical nucleotide sequence that allows formation of poly(A).poly(AalphaH(+))-like regions in acidic solutions. It is also inferred that the extent of ;hysteresis' might depend on the primary nucleotide sequence of rRNA as well as on secondary structure.

Adenine↗
PubMed1972

Long-lived conformation changes induced by electric impulses in biopolymers.

Electric impulses are capable of inducing long-lived conformational changes in (metastable) biopolymers. Results of experiments with poly(A).2 poly(U) and ribosomal RNA, which are known to develop metastabilities, are reported. A polarization mechanism is proposed to explain the structural transitions observed in the biopolymers exposed to the impulses. In accordance with this idea, the applied electric field (of about 20 kV/cm and decaying exponentially, with a decay time of about 10 musec) induces large dipole moments by shifting the ionic atmosphere of multistranded polynucleotide helices. This shift, in turn, causes strand repulsion and partial unwinding. The fields used in our experiments are of the same order of magnitude as those in nerve impulses. The significance of the impulse experiments with regard to the question of biological memory recording is briefly discussed.

Adenine Nucleotides↗