Alpha casein micelles show not only molecular chaperone-like aggregation inhibition properties but also protein refolding activity from the denatured state.

Casein micelles are a major component of milk proteins. It is well known that casein micelles show chaperone-like activity such as inhibition of protein aggregation and stabilization of proteins. In this study, it was revealed that casein micelles also possess a high refolding activity for denatured proteins. A buffer containing caseins exhibited higher refolding activity for denatured bovine carbonic anhydrase than buffers including other proteins. In particular, a buffer containing α-casein showed about a twofold higher refolding activity compared with absence of α-casein. Casein properties of surface hydrophobicity, a flexible structure and assembly formation are thought to contribute to this high refolding activity. Our results indicate that casein micelles stabilize milk proteins by both chaperone-like activity and refolding properties.

Enzyme-mediated protein refolding.

We employed a urease-catalyzed reaction to gradually remove a high concentration of a chaotropic agent (urea) from a denatured protein solution and demonstrated that efficient protein refolding can be achieved by the urease-catalyzed reaction, without large-volume dilution.

Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically at 303.2 K. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc. The Gibbs free energy change of the solubilizates from the aqueous bulk to the liquid solubilizate phase was evaluated from the dependence of their aqueous solubility on the alkyl chain length of the solubilizates, which leads to -3.46 kJ mol-1 for DeltaG(0)(CH), the energy change per CH2 group of the alkyl chain. The first stepwise solubilization constant (K(overline)1 ) was evaluated from the slope of the change of solubilizate concentration versus Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of the alkyl chain of the solubilizates, from which DeltaG(0,s)(CH2) as evaluated to be -2.71 kJ mol-1. The similar values above clearly indicate that the location of the alkyl chain is a hydrophobic micellar core, which is also supported by the absorption spectrum of the solubilized molecules.