Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity

Oxygen radical-mediated oxidation reactions of an alanine peptide motif - density functional theory and transition state theory study

<p>Abstract</p> <p>Background</p> <p>Oxygen-base (O-base) oxidation in protein backbone is important in the protein backbone fragmentation due to the attack from reactive oxygen species (ROS). In this study, an alanine peptide was used model system to investigate this O-base oxidation by employing density functional theory (DFT) calculations combining with continuum solvent model. Detailed reaction steps were analyzed along with their reaction rate constants.</p> <p>Results</p> <p>Most of the O-base oxidation reactions for this alanine peptide are exothermic except for the bond-breakage of the C_α-N bond to form hydroperoxy alanine radical. Among the reactions investigated in this study, the activated energy of OH α-H abstraction is the lowest one, while the generation of alkylperoxy peptide radical must overcome the highest energy barrier. The aqueous situation facilitates the oxidation reactions to generate hydroxyl alanine peptide derivatives except for the fragmentations of alkoxyl alanine peptide radical. The C_α-C_βbond of the alkoxyl alanine peptide radical is more labile than the peptide bond.</p> <p>Conclusion</p> <p>the rate-determining step of oxidation in protein backbone is the generation of hydroperoxy peptide radical via the reaction of alkylperoxy peptide radical with HO₂. The stabilities of alkylperoxy peptide radical and complex of alkylperoxy peptide radical with HO₂are crucial in this O-base oxidation reaction.</p

Thermolyses of <i>O</i>-phenyl oxime ethers. A new source of iminyl radicals and a new source of aryloxyl radicals

Six O-phenyl ketoxime ethers, RR\u2032C=NOPh 1-6, with RR\u2032= diaryl, dialkyl, and arylalkyl, together with N-phenoxybenzimidic acid phenyl ether, PhO(Ph)C=NOPh, 7, have been shown to thermolyze at moderate temperatures with "clean" N-O bond homolyses to yield iminyl and phenoxyl radicals, RR\u2032C=N. and PhO.. Since 1-6 can be synthesized at room temperature, these compounds provide a new and potentially useful source of iminyls for syntheses. The iminyl from 7 undergoes a competition between \u3b2-scission, to PhCN and PhO., and cyclization to an oxazole. Rate constants, 106 k/s-1, at 90 \ub0C for 1-6 range from 4.2 (RR\u2032 = 9-fluorenyl) to 180 (RR\u2032 = 9-bicyclononanyl), and that for 7 is 0.61. The estimated activation enthalpies for N-O bond scission are in satisfactory agreement with the results of DFT calculations of N-O bond dissociation enthalpies, BDEs, and represent the first thermochemical data for any reaction yielding iminyl radicals. The small range in k (N-O homolyses) is consistent with the known \u3c3 structure of these radicals, and the variations in k and N-O BDEs with changes in RR\u2032 are rationalized in terms of iminyl radical stabilization by hyperconjugation: RR\u2032C=N . \u2194 R.R\u2032C 61N. Calculated N-H BDEs in the corresponding RR\u2032C= NH are also presented.Peer reviewed: YesNRC publication: Ye

Uso de ensaios de microesclerometria instrumentada no estudo das propriedades da austenita expandida

A resistência à corrosão do aço inoxidável austenítico AISI 316 é usualmente acompanhada por propriedades mecânicas limitadas dessa liga. A austenita expandida, ou Fase-S, supersaturada em nitrogênio, endurece superficialmente o material, sem a formação de precipitados e consequente prejuízo da passivação, efeitos comumente observados nos métodos convencionais de endurecimento superficial. Caracterizações mecânicas dessa camada por ensaios de microesclerometria instrumentada fornecem um conjunto de dados empíricos relevantes para a compreensão e modelagem de fenômenos tribológicos atuantes em um dado sistema mecânico. O presente trabalho apresenta os resultados de uma série de ensaios de microesclerometria instrumentada realizados em amostras de aço AISI 316 nitretadas a plasma por 20 h em forno de corrente contínua, utilizando a tecnologia de tela ativa, temperatura de 400°C e atmosfera formada por três partes de nitrogênio para uma parte de hidrogênio (3N2:1H2). Também são discutidos a caracterização das amostras e demais resultados, como o reduzido coeficiente de atrito (< 0,1) e a ausência de falha adesiva da camad