Physiological chemistry and physics最新文献

Polymerization changes of tubulin (a contractile protein of brain) induced by temperature increase from 4 degrees C to 25 degrees C caused a large (85%) decrease in measured osmotic pressure of the tubulin. This indicates that contractile proteins within cells may be expected to play a significant role in cell osmotic equilibria.

A microwave heating method and an associated numerical method for computing the reaction velocities in a single experiment are proposed for rapid determination of the activation energy of enzymatic reactions. Application of this new technique to different enzymatic reactions is reported.

The phenomenon of transport of ions, sugars, amino acids, etc. across frog skin and other epithelial systems has been commonly interpreted on the basis of the membrane-pump theory, according to which asymmetry in solute distribution as well as transport into and out of all living cells results from the permeability properties and "pump" activities of the membrane. In the present review, certain findings in the field of transepithelial transport of solutes are given new interpretation on the basis of molecular mechanisms introduced in the association-induction hypothesis, according to which "active transport" of solutes occurs only across bifacial cell systems like frog skin and intestinal epithelium but not in the maintenance of steady levels of solutes in unifacial cell systems such as muscle, nerve, and red blood cells.

The EPR signal amplitude of human serum ceruloplasmin shows significant changes as a function of time and temperature during storage. The same behavior occurs with aqueous solutions of purified ceruloplasmin. From the observation that the spectral lines of the EPR signal of ceruloplasmin from unmanipulated serum are identical to those coming from purified ceruloplasmin, we conclude that only type I Cu2+ of ceruloplasmin are involved in the signal changes. A temperature-dependent electron shift toward type I Cu2+ paramagnetic centers, occurring via the type II and type III Cu2+ species of the protein, is believed responsible for the process. The possible origin of the reducing electrons is discussed. A procedure to obtain reproducibility of recording of EPR spectra of ceruloplasmin in physiological fluids is proposed.

We have predicted the secondary structure of horse muscle acylphosphatase by the statistical method of Chou and Fasman. In addition, we have studied the circular dichroism spectra of the enzyme, obtaining values for comparison to the predicted results. Discrepancies were found for the alpha-helix content estimated by the two methods.

Effect of pressure on activities of O-(2)-producing enzyme xanthine oxidase (XO) and O-(2)-scavenging enzyme superoxide dismutase (SOD) has been investigated to 1000 bar. Methods used included spectrophotometric determinations of inhibition by SOD of O-(2)-induced reduction of cytochrome c and oxidation of ascorbic acids. It was found that (1) pressure increases XO activity, the activation volume being delta V not equal to = -45 +/- 5 cm3/mol; and (2) pressure decreases SOD activity, the activation volume being delta V not equal to = 30 +/- 5 cm3/mol. Under the conditions of these experiments, pressure therefore favors an increase in O-(2) activity. This may lead to increased cell damage in organisms in high-pressure situations even if oxygen concentration is held constant.

Interaction of the synthetic lecithin dipalmitoylphosphatidylcholine (DPPC) smectic mesophases with sulfur-containing radioprotectors was investigated by means of spectrophotometric and dielectric measurements. Electrical conductivity behavior indicated in all cases that an electrostatic interaction occurs between DPPC and the antiradiation drugs. This interaction is very strong in the case of the WR 2721 molecule. Thermal transitions of DPPC studied by spectrophotometry and conductivity Arrhenius diagrams showed that although the radio-protectors investigated (except WR 2721) delete the pretransition of the lipid phase, the principal transition is not modified. The observed electrostatic interactions are discussed with regard to ionized sites of the phosphatidylcholine lipid head and those of the radioprotectors. The special cases of WR 2721 and its metabolite, WR 1065, are examined.

The human biological cell is a complex nonlinear system that behaves electrically as a double dipole. The nonlinear property of the cytoplasmic membrane permits is to divide; but it is the double-dipole property that motivates division and growth. Increasing the double-dipole moment increases speed of division. If the time required for division due to forces developed by the double-dipole becomes much less than the time needed for the chromatin material of the nucleus to properly develop and mature, defective genes will be formed, producing mutated daughter cells. Thus any stimulus that for prolonged periods increases the double-dipole moment can be responsible for producing mutated cells. One such stimulus is a "supercurrent" from an organic superconducting source. This supercurrent applied to tissue increases the cellular dipole moment, hence can produce an uncontrolled proliferation of biological cells giving rise to a tumor. In contrast, an injury current produces a controlled proliferation of embryonic cells in the traumatized area of the system. The latter proliferation is regulated by the negative feedback action of the host, which does not occur in the case of the supercurrent produced by an organic superconductor. Knowledge of the kind of organic superconductor involved, its transition temperature, and the critical magnetic field could make feasible a therapy aimed at terminating the offending supercurrent in the host.