Dissolution of the (100) face of octacalcium phosphate (OCP) single crystal in weak acidic solutions (pH = 6.5;25°C) was observed in situ using atomic force microscopy. Monomolecular steps (2.0 nm high) were o...Dissolution of the (100) face of octacalcium phosphate (OCP) single crystal in weak acidic solutions (pH = 6.5;25°C) was observed in situ using atomic force microscopy. Monomolecular steps (2.0 nm high) were observed;they originated from etch pits or crystal edges. Advancement of the dissolution process led to precipitation of nanoparticles as small as ~10 nm even though the solution was undersaturated with respect to OCP. This precipitation of nanoparticles was accompanied by a drastic decrease in the dissolution rate;however, the substrate OCP continued to dissolve, indicating that dissolution and growth occurred simultaneously on the same surface. The precipitated nanoparticles coalesced and eventually covered the entire surface without changing the surface morphology of the substrate crystal. The step height after complete coverage was ~2.0 nm, the same as that observed on the dissolving OCP surface. These findings indicate that the precipitated phase was a pseudomorph of OCP crystal.展开更多
Crystallization of enzymes in presence of impurities is important for clarifying the role of enzymes in natural world. Although it is proposed that impurities inhibit nucleation of enzyme crystallization, details are ...Crystallization of enzymes in presence of impurities is important for clarifying the role of enzymes in natural world. Although it is proposed that impurities inhibit nucleation of enzyme crystallization, details are unclear. In this study, crystallization of cellobiohydrolase from Aspergillus niger was investigated by dynamic and time-resolved static light scattering using cellobiose as an impurity. We aimed to clarify how cellobiose inhibits cellobiohydrolase crystallization and to crystallize cellobiohydrolase in concentrated cellobiose without using seeds. The contribution of attractive forces to total intermolecular interactions of cellobiohydrolase monomers increased with the molar ratio of cellobiose/cellobiohydrolase (R(cb/ce)). Association dynamics of cellobiohydrolase using lithium sulfate, however, showed that the initial aggregation rate decreased with an increase in R(cb/ce). Because binding sites of cellobioses to cellobiohydrolase molecules differed from those for the growth of protein crystals, the binding of cellobioses would increase the chemical potential of the cellobiohydrolase monomers, which gradually reduced supersaturation for growth as the aggregate size increased. This result was in contrast with the conventional idea that cellobiose inhibits the nucleation of cellobiohydrolase crystals. Gentle agitation of cellobiose-containing cellobiohydrolase solutions during sitting-drop vapor-diffusion growth resulted in the growth of cellobiohydrolase single crystals for all R(cb/ce) conditions without using seeds.展开更多
文摘Dissolution of the (100) face of octacalcium phosphate (OCP) single crystal in weak acidic solutions (pH = 6.5;25°C) was observed in situ using atomic force microscopy. Monomolecular steps (2.0 nm high) were observed;they originated from etch pits or crystal edges. Advancement of the dissolution process led to precipitation of nanoparticles as small as ~10 nm even though the solution was undersaturated with respect to OCP. This precipitation of nanoparticles was accompanied by a drastic decrease in the dissolution rate;however, the substrate OCP continued to dissolve, indicating that dissolution and growth occurred simultaneously on the same surface. The precipitated nanoparticles coalesced and eventually covered the entire surface without changing the surface morphology of the substrate crystal. The step height after complete coverage was ~2.0 nm, the same as that observed on the dissolving OCP surface. These findings indicate that the precipitated phase was a pseudomorph of OCP crystal.
文摘Crystallization of enzymes in presence of impurities is important for clarifying the role of enzymes in natural world. Although it is proposed that impurities inhibit nucleation of enzyme crystallization, details are unclear. In this study, crystallization of cellobiohydrolase from Aspergillus niger was investigated by dynamic and time-resolved static light scattering using cellobiose as an impurity. We aimed to clarify how cellobiose inhibits cellobiohydrolase crystallization and to crystallize cellobiohydrolase in concentrated cellobiose without using seeds. The contribution of attractive forces to total intermolecular interactions of cellobiohydrolase monomers increased with the molar ratio of cellobiose/cellobiohydrolase (R(cb/ce)). Association dynamics of cellobiohydrolase using lithium sulfate, however, showed that the initial aggregation rate decreased with an increase in R(cb/ce). Because binding sites of cellobioses to cellobiohydrolase molecules differed from those for the growth of protein crystals, the binding of cellobioses would increase the chemical potential of the cellobiohydrolase monomers, which gradually reduced supersaturation for growth as the aggregate size increased. This result was in contrast with the conventional idea that cellobiose inhibits the nucleation of cellobiohydrolase crystals. Gentle agitation of cellobiose-containing cellobiohydrolase solutions during sitting-drop vapor-diffusion growth resulted in the growth of cellobiohydrolase single crystals for all R(cb/ce) conditions without using seeds.
