Physiological chemistry and physics最新文献

Interactions amond DNA, phospholipids, and Cu2+ ions have been investigated by means of thermal denaturation technique. The results indicate that phosphatidylserine and sphingomyelin interact with Cu2+ ions, which are able to prevent the chance of binding of the phospholipids to the double helix. This interaction is strictly dependent upon the concentration of the divalent cation and reduces the capability of the employed phospholipids to modify the thermal stability of DNA.

The effect of pressure on the catalytic decomposition of hydrogen peroxide by catalase has been investigated to 1000 bar by spectrophotometry and oxygen polarography. Comparison between the two methods showed good agreement up to 700 bar but increasing deviation above that pressure. The kinetic behavior of catalase is rather complicated and difficult to interpret. For small peroxide concentrations the reaction rate increased with pressure below 500 bar. For higher concentrations the rate decreased at all pressures. Temperature had no marked effect on the pressure behavior but addition of KCl led to a large increase in activation volume.

Among carbohydrates, D-glucose, D-mannose, D-galactose, and glycogen yielded a previously described fluorescent pigment, reddish in alkaline medium and yellowish in acid, when heated with L-cysteine in hydrochloric acid solution. D-Fructose and some pentoses yielded other patients. Among tissue hydrolysates, liver, small intestine, brain, and spleen were found rich in the cysteine pigment but little or none was produced from skeletal muscle, blood, or urine. Among subfractions of rat liver cells, the microsomal fraction proved the richest source of the pigment in nmol/mg protein, though the total yield from the soluble fraction was comparable to that from the microsomal fraction. In the latter fraction, only ribosomal particles yielded the pigment; smooth membrane did not. The pigment yield from yeast was comparable to that from liver. Yield from Escherichia coli K-12 was about one-forth that from yeast.

Glutathione has been proposed as responsible for amino acid transport across the brush border membrane of the kidney. According to the gamma glutamyl cycle hypothesis, gamma glutamyl transpeptidase, an enzyme bound to brush border membranes, interacts with intracellular glutathione and an extracellular amino acid, incurring formation of gamma glutamyl-amino acid which is then transported into the cell. The hypothesis further holds that glutathione levels are held constant by a reaction cycle involving 5 cytosolic enzymes and the utilization of 3 moles of ATP. We evaluated this hypothesis, using a brush border vesicle system from rabbit renal proximal tubule. The vesicles enabled study of the transport of L-methionine in a system free of other factors that might influence glutathione. The results suggest that glutathione alone does not enhance the influx of methionine.

From quantum mechanical and relativity principles applied to an observer using a bounded superconductive detector, any magnetic or electric field, which superficially may appear steady and homogeneous, should be perceived to have a wavelength and frequency which are functions of the size of the detector as well as of the energy density of the field. From the Heisenberg uncertainty principle, equations are derived for the uncertainties of measurement of field energy and of detector size as imposed by the principles of quantum mechanics, even if the instruments of measurement are perfect. If energy density is sufficiently low and/or size of detector is sufficiently small, then numerical values and geometries of the fields become unmeasurable by any experimental method but topological properties of the system may still be measurable. A method for estimation of size of superconductive microregions in materials or in living systems is derived. It is calculated that if superconductive microdetectors exist in living systems capable of detection of 0.1 to 1.0 gauss magnetic fields, then minimum superconductive detector diameters of 7.9 and 2.6 microns respectively are required, and these magnetic fields will have perceived effects equivalent to wavelengths of 7.9 and 2.6 microns respectively (the infrared region of light). The estimated detector sizes are comparable with the sizes of mitochondria, melanin granules, and retinal rods.

Proton spin-lattice relaxation times (T1) for normal tissues and cultured cells, and for neoplastic tissues and transformed culture cells, were measured. Increases in T1 of neoplastic tissue and normal tissues of mice with neoplasms were observed. No difference was found between T1 of normal 3T3 cells and of an SV40 viral transformed cell line. These data imply that changes in T1 of neoplastic tissue may not be due to intrinsic properties of cancerous cells but rather to physiological interaction of the neoplasm with its physiological environment. The measurement of several tissues of rat showed a good correlation between T1 and tissue water content, and addition of water by glass capillary increased T1 of samples. For samples in sealed NMR tubes, however, changes in T1 were incurred by boiling, freezing, or storage at various temperatures. These data imply that changes in T1 may be influenced by cellular water content as well as macromolecular conformation.

To clarify contributions to cellular transmembrane potential concentration potentials of phospholipid bilayer membranes and surface potentials of phospholipid monolayers were measured with respect to salt concentrations and various surface charge densities. For highly charged membranes of symmetrical surface charge density, it was found that the observed transmembrnae potentials are due mostly to the difference between the surface potentials on each side of the membrane. For uncharged membranes, it was found that the transmembrane potential is due to the ion diffusion potential across the membrane. Also discussed are ion permeabilities through the membrane in relation to transmembrane potential.

The binding isotherms for Triton X-100 binding to equine and rabbit serum albumin were determined by equilibrium dialysis at 16 degrees C in pH 7.0, I = 0.05 phosphate buffer. Presented in a Scatchard plot, the binding isotherms are a straight line, indicating thermodynamically independent and identical binding sites. In this model equine serum albumin is characterized as having 11 such sites with an equilibrium constant of 6.0 x 10(3) M-1. Similarly, rabbit serum albumin is characterized as having 9 such sites with an equilibrium constant of 8.0 x 10(3) M-1.

Fundamental assumptions of the chemiosmotic hypothesis of Mitchell are examined. Comparison of these assumptions with experimental data accumulated over the past fifty years leads to the conclusion that the hypothesis has not been supported. A review of important findings concerning the physical state of the major intracellular cation potassium shows clearly that this ion does not exist in a free state but is adsorbed on specific anionic sites. These findings refute the membrane-pump theory but added powerful support for the association-induction hypothesis, on the basis of which a new mechanism of oxidative phosphorylation as well as a wide variety of mitochondrial behaviors are proposed and compared with experimental data.

Bovine serum albumin (BSA) interacts with PGBx, a polymeric derivative of 15-keto-prostaglandin B1, to form a complex that does not exhibit the fluorescence of free BSA. The complex is soluble at pH 5.2 in contrast to free PGBx, which is insoluble. Molar ratio of the BSA-PGBx complex is 1:18. This complexing appears to suppress the ability shown by non-complexed PGBx to reactivate phosphorylation in degraded isolated rat liver mitochondria.