alpha-chymotrypsin and lactitol

The relationship between protein conformational stability in aqueous solution and the magnitude of lyophilization-induced structural changes was investigated employing alpha- and gamma-chymotrypsin. As a measure of the conformational stability the melting temperature T(m) was determined in distilled water at various pH values. The proteins were then lyophilized from those pH values where the conformational stability was maximum (pH 4.5) and minimum (pH 7.8). Protein secondary structure was quantitatively determined utilizing Fourier-transform infrared spectroscopy employing two regions sensitive to protein structure, the amide-I (1600-1700 cm(-1)) and amide-III (1215-1335 cm(-1)). Lyophilization induced significant structural alterations in both proteins, characterized by a slight decrease in the alpha-helix and a significant increase in the beta-sheet content. However, regardless of the pH from which the proteins were lyophilized, the secondary structures in the solid state were indistinguishable. This result shows that there is no relationship between the conformational stability in aqueous solution and the magnitude of lyophilization-induced structural changes. We also investigated whether lyoprotectants could minimize lyophilization-induced structural changes by increasing protein conformational stability in aqueous solution. After having identified trehalose as being efficient in largely preventing lyophilization-induced structural alterations, we conducted co-lyophilization experiments from various pH values. The results obtained exclude any contribution from increased protein conformational stability caused by the additive in aqueous solution to the beneficial structural preservation upon lyophilization. This can be understood because the dehydration and not the freezing process, as shown in an air-drying experiment, mainly causes protein structural alterations.

Topics: Chymotrypsin; Enzyme Stability; Freeze Drying; Hydrogen-Ion Concentration; Lactose; Protein Conformation; Protein Structure, Secondary; Solutions; Spectroscopy, Fourier Transform Infrared; Sugar Alcohols; Trehalose; Water

Lactitol-based cross-linked hydrogel was synthesized, and model proteins (alpha-chymotrypsin, beta-lactoglobulin, bovine serum albumin (BSA), and gamma-globulin) were incorporated into the cross-linked hydrogel. The larger-molecular-weight proteins have lower diffusivity (D(e)) in the hydrogel. Increasing temperature accelerated the diffusion rate of proteins; however, the diffusion did not follow the Arrhenius equation at temperatures above 37 degrees C. The swelling ratio of the hydrogel was slightly decreased after heating for 2 h at 37 and 45 degrees C, and significantly reduced after 1 h at 60 degrees C. Therefore, diffusion of beta-lactoglobulin and BSA may be decreased by hydrogel shrinking at temperature over 37 degrees C. The model proteins have high affinities to buffer solution compared to the hydrogel network structure, resulting in high partition coefficients (K > 1) which do not affect the calculation of D(e) values. Incorporated protein release follows the theory of hindered diffusion.

Topics: Animals; Cattle; Chymotrypsin; Cross-Linking Reagents; Diffusion; gamma-Globulins; Hot Temperature; Hydrogels; Lactoglobulins; Proteins; Serum Albumin, Bovine; Sugar Alcohols; Thermodynamics