RESUMO
Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in static and dynamic light scattering experiments. We show that at high pressure casein micelles decompose into small fragments comparable in size to casein monomers. At intermediate pressure we observe particles measuring 15 to 20 nm in diameter. The stability against pressure dissociation increased with temperature, suggesting enhanced hydrophobic contacts. The pressure transition curves are biphasic, compatible with a temperature (but not pressure)-dependent conformational equilibrium of two micelle species. Our thermodynamic model predicts an increase in structural entropy with temperature.
Assuntos
Caseínas/química , Micelas , Temperatura Alta , Concentração de Íons de Hidrogênio , Pressão Hidrostática , Luz , Modelos Químicos , Fragmentos de Peptídeos/química , Espalhamento de Radiação , TermodinâmicaRESUMO
The pressure sensitivities of the near infrared spectra of the light-harvesting (LH2) complex and a mutant complex with a simplified BChl-B850 binding pocket were compared. In the mutant an abrupt change in the spectral properties occurred at 250 MPa, which was not observed with the native sample. Increased disorder due to collapse of the chromophore pocket is suggested.
Assuntos
Escherichia coli/genética , Pressão Hidrostática , Complexos de Proteínas Captadores de Luz/genética , Mutação/genética , Rhodobacter sphaeroides/genética , Espectroscopia de Luz Próxima ao Infravermelho , Complexos de Proteínas Captadores de Luz/química , Modelos MolecularesRESUMO
Pressure-induced dissociation of a turbid solution of casein micelles was studied in situ in static and dynamic light scattering experiments. We show that at high pressure casein micelles decompose into small fragments comparable in size to casein monomers. At intermediate pressure we observe particles measuring 15 to 20 nm in diameter. The stability against pressure dissociation increased with temperature, suggesting enhanced hydrophobic contacts. The pressure transition curves are biphasic, compatible with a temperature (but not pressure)-dependent conformational equilibrium of two micelle species. Our thermodynamic model predicts an increase in structural entropy with temperature.
Assuntos
Caseínas/química , Micelas , Temperatura Alta , Concentração de Íons de Hidrogênio , Pressão Hidrostática , Luz , Modelos Químicos , Fragmentos de Peptídeos/química , Espalhamento de Radiação , TermodinâmicaRESUMO
The pressure sensitivities of the near infrared spectra of the light-harvesting (LH2) complex and a mutant complex with a simplified BChl-B850 binding pocket were compared. In the mutant an abrupt change in the spectral properties occurred at 250 MPa, which was not observed with the native sample. Increased disorder due to collapse of the chromophore pocket is suggested.