RESUMO
Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight.
Assuntos
Hidrogênio , Gelo , Marte , Atmosfera , Gelo-Seco , Meio Ambiente Extraterreno , Raios gama , Modelos Teóricos , Nêutrons , Astronave , Espectrometria gama , Análise Espectral , ÁguaAssuntos
Assistência ao Convalescente/métodos , Angioplastia Coronária com Balão/psicologia , Angioplastia Coronária com Balão/reabilitação , Atitude Frente a Saúde , Isquemia Miocárdica/terapia , Avaliação das Necessidades , Avaliação em Enfermagem/métodos , Educação de Pacientes como Assunto/métodos , Recuperação de Função Fisiológica , Idoso , Idoso de 80 Anos ou mais , Angioplastia Coronária com Balão/efeitos adversos , Angioplastia Coronária com Balão/enfermagem , Estudos Transversais , Análise Ética , Feminino , Comportamentos Relacionados com a Saúde , Conhecimentos, Atitudes e Prática em Saúde , Humanos , Estilo de Vida , Masculino , Pessoa de Meia-Idade , Recidiva , Fatores de Tempo , Resultado do TratamentoRESUMO
Glutathione reductase from Escherichia coli is inactivated when incubated with either NADPH or NADH. The process is inversely dependent on the enzyme concentration. Inactivation is rapid and monophasic with 1 microM NADPH and 1 nM enzyme FAD giving a t1/2 of 1 min. Complex formation between NADPH and the two-electron reduced enzyme (EH2) at higher levels of NADPH protects against rapid inactivation. NADP+, produced in a side reaction with oxygen, also protects by forming a complex with EH2. These complexes make analysis of the concentration dependence of the inactivation process difficult. Inactivation with NADH, where complexes do not interfere, is slower but can be analyzed more readily. With 152 microM NADH and 5.4 nM enzyme FAD, the time required for 50% inactivation is 17 min. The process is markedly biphasic, reaching the final inactivation level after 5-7 h. Analysis of the relationship between the final level of inactivation with NADH and the enzyme concentration indicates that inactivation is due to dissociation of the normally dimeric enzyme. Thus, the position of the dimer-monomer equilibrium between an active dimeric two-electron reduced species and an inactive monomeric two-electron reduced form determines the enzyme activity. An apparent equilibrium constant (Kd) for dissociation of dimer obtained from the anaerobic concentration dependent inactivation curves is 220 nM. Enzyme inactivated with NADH can be reactivated with glutathione, and the reactivation kinetics are second order, monomer-monomer over 75% of the reaction with an average apparent association rate constant (ka) of 13.1 (+/- 5.5) X 10(6) M-1 min-1.