Physiological chemistry and physics最新文献

Peroxidase, isolated from B16 mouse melanoma, converted tyrosine to dopachrome in the presence of either dopa or dihydroxyfumarate co-factor. A suspended homogenate of cloned, cultured B16 mouse melanoma cells also showed peroxidatic conversion of tyrosine to dopachrome in the presence of dihydroxyfumarate co-factor. The findings confirm previous histochemical, autoradiographic-histochemical, and EM-histochemical studies showing that melanoma peroxidase can convert tyrosine to melanin.

Basic semiconductor characteristics of natural melanins isolated from bovine eye, human dark hair, and banana peel were obtained by means of the dc dark conductivity experiments and optical absorption measurements. The results were compared with results obtained for synthetic melanin. Specific conductivity in natural melanins is of the order 10(-11) omega -1 cm-1 and in synthetic melanin 10(-8) omega -1 cm-1. Thermal activation energies in the range 298-333 degrees K are eye melanin, 0.93 eV; hair melanin, 1.01 eV; banana melanin, 1.04 eV; whereas synthetic melanin has two values of activation energy: up to 311 degrees K, 0.1 eV; above 313 degrees K, 0.78 eV. Optical gaps are: in eye melanin, 1.73 eV; in hair melanin, 1.35 eV; in banana melanin, 1.55 eV; and in synthetic melanin, 1.40 eV. The observed differences between natural melanins and the synthetic one could be explained by either the presence of protein residues in natural melanins or the influence of the isolation method on their electrical properties.

Suspensions of phospholipid liposomes (phosphatidylcholine, phosphatidylglycerol, phosphatidylethanoline and phosphatidylserine) were examined by colloid titration with polydiallyldimethylammonium chloride and potassium polyvinylsulfate as polycationic and polycationic and polyanionic titrants, respectively. In addition, the electrophoretic mobilities of the liposomes were measured with a cytopherometer. The following conclusions are drawn from the results of the titration: Phosphate and ammonium groups of phosphatidylcholine in liposomes form intramolecular or intermolecular salt linkages. Phosphate on the surface of phosphatidylglycerol liposomes shows a constant dissociation at above pH 3. Liposomes of phosphatidylethanolamine have no charge at low pH and a maximum negative charge above pH 10.5. On the surface of phosphatidylserine liposomes, the carboxyl group is completely dissociated at pH 6-7 and the phosphate group is released completely by the conversion of the ammonium ion to an amino group above pH 10.5. Stemming from these results, colloid titration can reveal the dissociation or the situation on the surface of liposomes more precisely than electrophoresis. Thus colloid titration is useful for determining the states of functional groups on the surface of phospholipid liposomes.

Continuous measurements of local blood flow were performed by means of short pulse heated miniature thermistors. Results obtained in rat cerebral cortex or skeletal muscle show good stability of the recordings and the sensitivity of the system to phasic changes in local blood flow. Experiments on perfused rabbit kidney support the possibility of using this method for quantitative measurements.

The active species of aspartase from Escherichia coli is further 3-5 fold activated upon limited proteolysis with trypsin releasing carboxy-terminal peptides as reported previously (N. Yumoto, M. Tokushige, and R. Hayashi. Biochim. Biophys. Acta, 616, 319 (1980) ). Survey of the protease specificity for the activation revealed that subtilisin BPN' and several other proteases having far broader substrate specificity than trypsin also activated the enzyme. The results of sequence analyses revealed that subtilisin BPN' cleaved mainly the serylarginine bond near the carboxy-terminal and released an octapeptide, while trypsin cleaved mainly the arginyltyrosine bond which is just next to the subtilisin cleavage site. These results suggest that the protease-mediated activation does not necessarily require a site-specific peptidyl cleavage, but the cleavage of any bond within a certain region centered at arginine, the eighth residue from the carboxy-terminal, is sufficient.

Polymeric prostaglandin PGBx normalizes the high blood sugar seen in hereditary diabetic mice. PGBx does not enhance the sensitivity of these mice to the hypoglycemic effect of insulin. It is therefore proposed that the hypoglycemic effect of PGBx may be an indirect consequence of induction of increased consumption by genetically defective mitochondria of two and three carbon fragments produced at the bottom of the glycolysis chain.

L-Lanthionine is oxidized by snake venom L-amino acid oxidase with the release of one mole of ammonia per mole of lanthionine. Spectrophotometric, chromatographic, and analytical properties are all consistent with the identification of the mono-keto derivative of lanthionine as the first enzymatic product of the reaction. This then cyclizes into a dihydrothiazine dicarboxylic acid which is further subject to spontaneous changes. Authentic samples of the thiazine derivative have been prepared by interacting L-cysteine with bromopyruvic acid. The properties of the synthetic product are described and compared with those exhibited by the enzymatic product.

Tissue freezing without tissue death commonly shows ice formation in water outside but not inside of the cells. This observation conflicts with the expectation derived from the classical picture of the cell as a bag of liquid water with equal osmotic pressures and therefore equal depression of freezing points on both sides of the cell membrane. However, if intracellular water is structured in the form of multiple polarized layers adsorbed on cell proteins in accord with the Bradley isotherm, the prediction of theory is in harmony with experimental data.

Light emission (chemiluminescence, CL) from model reactions in vitro, relevant to the formation and degradation of melanins has been investigated. On the basis of chemiluminescence kinetics and spectra, absorption and fluorescence changes and semi-empirical calculations, it has been shown that the common exergonic step of the chemiexcitation is the oxidative opening of the six-membered ring of indoloquinone. The data indicating cytotoxic agents formation such as H2O2 O2- and 1O2 as well as the energy transfer to strong fluorescers are presented. Physiological implications of the generation of excited molecules during the biosynthesis and degradation of melanins are discussed in terms of "photobiochemistry without light."