Physiological chemistry and physics最新文献

Measurements of optical absorption of synthetic and natural melanins during their degradation in sodium hydroxide establish that from the "optical" point of view these polymers consist of two different parts. An explanation of this result and its possible relation to the biological role of melanin is given.

In contracting (superprecipitating) clearing and fully contracted (previously superprecipitated) actomyosin molecules the presteady state phosphate burst was found to be 2 nanomoles inorganic phosphate (Pi) per nanomole myosin. In these muscle models a significant difference in the Mg2+ ATPase activity was found following the initial phosphate burst. Between 120 and 800 milliseconds after the commencement of the reaction the Mg2+ ATPase activity of contracting actomyosin molecules was 5-10 times greater than that of the fully contracted or clearing actomyosin molecules. In the same time interval the rate of turbidity increase of the contracting actomyosin molecules was about 10 fold greater than during the remainder of the time to reach maximal superprecipitation. This high initial ATPase activity found to be present only in the contracting actomyosin molecules and coinciding with the high rate of the velocity of contraction provides sufficient energy for contraction. We propose that this high Mg2+--ATPase activity following the initial burst and included as a part of "conventional" steady state ATPase activity is the source of energy for muscular contraction. Calculation of kinetic and thermodynamic constants indicates that the contracting actomyosin molecule is subjected to a conformational change. As a consequence of contraction the complementarity of the enzyme site to the intermediate complex decreases about 100 fold. Thus the contracted molecules temporarily become relatively refractive to provide energy for the contractile process. In our opinion these findings are important with regard to muscular contraction.

A series of temperature cycling experiments during Radiofrequency Radiation (RFR) exposure of rats was performed. It is evident that this type of exposure procedure permits the introduction of high doses of electromagnetic energy into biological systems while the systems are maintained at physiologically acceptable temperatures. Experiments were carried out at various power densities (50-200 mW/cm2) using continuous wave (CW) and pulsed radiation while the carrier frequency was maintained at 2.06 GHz. It was observed that single-day RFR exposures at power levels used in this series produced no observable effect on temperature regulation of rats in terms of heat dissipation efficiency.

The present study was undertaken to critically examine whether the dilating action of inhalation anesthetics is specific to lipid membranes. Delipidated crystalline bovine serum albumin was used as a model and the density of a salt-free aqueous solution was measured by a high-precision oscillation densimeter. The partial molal volumes of albumin at infinite dilution were 50,326, 51,019 and 51,698 cm3 . mol-1, respectively at 293, 308 and 323 degrees K. From the difference between the present value and the volume of dry albumin, the number of electrostricted water molecules at the surface of albumin in aqueous solution at 293.15 degrees K is estimated to be about 720. Addition of diethylether to the albumin solution increased the partial molal volume of albumin, dose-dependently. At 57.88 mmolal, diethylether expanded the partial molal volume of albumin at 293 degrees K by 295 cm3 . mol-1 or 0.59%. This volume expansion does not include the space occupied by the anesthetic molecules in albumin. If the expansion can be assumed to be caused mainly by melting of electrostricted water molecules, about 110 water molecules were released from the protein surface. The partial molal volume of diethylether was increased when bound to albumin. The increase indicates that the contact between diethylether and water is partially destroyed and that high pressure squeezes out anesthetic molecules from the protein.

Chemical parametric excitation is presented as the fundamental mechanism of energy transfer. Together with the Franck-Condon principle, it provides a mechanically sound explanation for enzymatic reaction, nerve excitation, muscle contraction, and electron transfer at a basic level. Intermediate between macroscopic models of membrane asymmetry and molecular models, the new model rests on a systematic approach, proposed here, to organizational aspects of the energy transfer processes. In support, a derivation is given of the chemical analog of the Manley-Rowe power conservation relations for parametrically excited electrical networks. This extension to chemical systems indicates for the first time an explanation of power flow directionality and delegates a pumping role to the enzyme. The generalized Manley-Rowe relations are suggested to be a universal law of nature. In such case, nonlinearity could be attributable to the coupling of three systems by these generalized Manley-Rowe conditions relating flows/reactions/oscillations--even though separately each system might be described by linear (Onsager) relations.

Near-infrared 700-950 absorbance of some chromophores has been measured in different biological tissues, in particular rat and rabbit brain, to assess value of this noninvasive technique for monitoring of the regional functional state. Experiments carried out under different induced circulatory conditions confirmed the possibility of obtaining information on local blood content and hemoglobin oxygenation level as well as an indication of redox state of cytochrome c oxidase, the enzymatic complex that catalyzes about 95% of cellular oxygen consumption. The near IR spectral data were correlated with the result of independent simultaneous measurements of circulatory function: blood pressure, local blood flow, and local blood volume.

1H-nuclear magnetic resonance (NMR) was used for the study of aerobic glucose metabolism in Toxoplasma gondii harvested from the peritoneal exudate of experimentally infected mice. Without any pretreatment (i.e., extraction, separation or purification) of the supernatant fluids from the cell suspension incubated with glucose for various time intervals, we were able to identify and quantitate the end-products of glucose metabolism by means of 1H-NMR. The major end-products found were lactic acid and acetic acid.

The influence of constant homogeneous magnetic fields (700 to 13,000 gauss) on cytochrome c oxidase activity as a function of strength and duration of magnetic field and as a function of enzyme concentration at 0-5 degrees C in solution was measured on samples not moved or moved relative to the magnetic field lines. Increases or decreases of enzyme activity were observed depending on whether or not the samples were so moved. These changes persisted for hours after terminating exposure to the magnetic field.

Analyses of the diffusible fraction of serum for sodium, potassium, and chloride have indicated that the ratios of the levels of the protein solution to those of the filtrate do not follow the predicted Donnan values. Specifically, measurements by sodium glass electrode showed that sodium activities are the same for both protein solution and filtrate in contradiction to the Donnan model which predicts greater activity for the sodium in the protein solution because of its greater analyzed content. An alternative model that fits the experimental findings is discussed, and calculations made possible by this model are presented that give reasonable values for bound sodium, bound water, and a radius for an assumed spherical albumin molecule. A review of Donnan's original data discloses discrepancies in his assumptions.