No abstract

Hemoblogin (Hb), which is a typical oligomeric protein, was introduced into the pores of mesoporous silica (FSM: folded-sheet mesoporous material) that had a diameter of 7.5 nm. Soret CD spectra of Hb-FSM-7.5 conjugates showed a peak that was identical to that of free Hb. This suggests that Hb retained its highly ordered structure in the mesoporous silica. In addition, the UV-visible absorption spectrum showed that Hb had an increased resistance to heat denaturation in the silica. Even after heat treatment at 85 degrees C, Hb-FSM-7.5 retained its ligand-binding activity. The stability of Hb-FSM-7.5 was examined further by measuring its peroxidase-like activity. Encapsulation of Hb resulted in the retention of activity in the presence of high NaCl or Gdn-HCl levels. This suggests that encapsulation prevented dissociation and denaturing. Thus, it seems that the mesopores created a favorable environment for the oligomeric protein to perform its function, even under harsh conditions.

The silica precipitation activity of lysozyme and the possibility of controlling the resulting particle morphologies were investigated. Lysozyme can act as not only a silica precipitation agent but also as a component of the precipitation products, namely, forming a composite of lysozyme and silica. Stirring produced lysozyme−silica hybrid granular particles (L-SHGs), while a sonochemical treatment resulted in lysozyme−silica hybrid hollow particles (L-SHHs). The silica precipitation activity of lysozyme and the formation of L-SHHs occur only around pH 9. At the optimized pH, the lysozyme concentration was found to affect the morphologies of the L-SHHs. Compared with other basic proteins, the foaming properties of lysozyme appear to be a key factor in the formation of hollow structures. The proposed formation mechanisms of L-SHGs and L-SHHs are also discussed.