RESUMO
The preparation of suitably large protein single crystals is essentially the rate-determining step of protein x-ray structure determinations. Attempts to produce single crystals with two model compounds-beta-galactosidase and lysozyme-under conditions of microgravity were successful. Crystals formed by salting out from solutions kept free of convection were 27 and 1000 times larger in volume, respectively, than those produced in the same apparatus but exposed to terrestrial gravitation.
RESUMO
Two competitive inhibitors of beta-D-galactosidase activity, namely, 2,6-anhydro-S-[ethylmercury(II)]-1-thio-D-glycero-L-manno-heptitol (4) and bis(2,6-anhydro-1-thio-D-glycero-L-manno-heptitol)mercury(II) (6), with inhibition constants of 8.0 X 10(-4) M and 1.9 X 10(-4) M, were synthesized. Compound 6 was incorporated into the crystalline enzyme by cocrystallization. The stoichiometry of the enzyme-inhibitor complex was 1:4, corresponding to one molecule of inhibitor per active site of the enzyme. Compound 4 was found to be unstable against X-ray irradiation, whereas compound 6 was submitted to X-rays for several days without any radiation damage.
Assuntos
Escherichia coli/enzimologia , Compostos de Etilmercúrio/síntese química , Galactosidases/antagonistas & inibidores , Álcoois Açúcares/síntese química , beta-Galactosidase/antagonistas & inibidores , Compostos de Alquilmercúrio/síntese química , Compostos de Alquilmercúrio/farmacologia , Compostos de Etilmercúrio/farmacologia , Indicadores e Reagentes , Cinética , Relação Estrutura-Atividade , Álcoois Açúcares/farmacologiaRESUMO
Concentrations of airborne coliform bacteria as high as 1.5 X 10(4) m-3 were observed 8 cm above anaerobically digested sewage sludge applied to a forest clearcut. Dry conditions and high wind speeds tended to favor aerosol generation.
Assuntos
Microbiologia do Ar , Escherichia coli/isolamento & purificação , Esgotos , Aerossóis , Umidade , Chuva , Estações do Ano , Luz Solar , Temperatura , VentoRESUMO
Comparisons of the amino acid compositions of the nitrogenase proteins from different organisms and their correlation with cross-reactivities and taxonomical data suggest an evolution within bacterial genomes rather than within plasmids. Comparisons of the amino acid compositions of nitrogenases and other ATP-ases show similarities which might be due to the evolution of these ATP-ases from a common ancestral protein.