Correlation between thermal aggregation and stability of lysozyme with salts described by molar surface tension increment: an exceptional propensity of ammonium salts as aggregation suppressor

Protein aggregation is a critical problem for biotechnology and pharmaceutical industries.Despite the fact that soluble proteins have been used for many applications, our understandingof the effect of the solution chemistry on protein aggregation still remains to be elucidated.This paper investigates the process of thermal aggregation of lysozyme in the presence ofvarious types of salts. The simple law was found; the aggregation rate of lysozyme increasedwith increasing melting temperature of the protein (Tm) governed by chemical characteristicsof additional salts. Ammonium salts were, however, ruled out; the aggregation rates oflysozyme in the presence of the ammonium salts were smaller than the ones estimatedfrom Tm. Comparing with sodium salts, ammonium salts increased the solubility of thehydrophobic amino acids, indicating that ammonium salts adsorb the hydrophobic region ofproteins, which leads to the decrease in aggregation more effectively than sodium salts. Thepositive relation between aggregation rate and Tm was described by another factor such as thesurface tension of salt solutions. Fourier transform infrared spectral analysis showed thatthe thermal aggregates were likely to form b-sheet in solutions that give high molar surfacetension increment. These results suggest that protein aggregation is attributed to the surfacefree energy of the solution

Study on the Principle of Photosynthetic Light Energy Conversion Based on Divergence of Chlorophyll Molecules

The composition of photosystem II (PSII) in the chlorophyll (Chl) d-dominatedcyanobacterium Acaryochloris marina MBIC 11017 was investigated to enhance the generalunderstanding of the energetics of the PSII reaction center. We first purifiedphotochemically active complexes consisting of a 47 kDa chlorophyll protein (CP47), CP43’(PcbC), D1, D2, cytochrome b559, PsbI, and an unknown small polypeptide. The pigmentcomposition per two pheophytin (Phe) a molecules was 55 ± 7 Chl d, 3.0 ± 0.4 Chl a, 17 ± 3α-carotene, and 1.4 ± 0.2 plastoquinone-9. A special pair was detected by a reversibleabsorption change at 713 nm (P713) together with a cation radical band at 842 nm. FTIRdifference spectra of the specific bands of a 3-formyl group allowed assignment of the specialpair. The combined results indicate that the special pair includes a Chl d homodimer.The primary electron acceptor was shown by photoaccumulation to be Phe a, and itspotential was shifted to a higher value than that in the Chl a/Phe a system. The overallenergetics of PSII in the Chl d system adapt to changes in the redox potentials, with P713as the special pair utilizing lower light energy at 713 nm. Our findings support the ideathat changes in photosynthetic pigments combine with modification of the redox potentialsof electron transfer components to give rise to energy changes in the total reaction system.■原 著■ 2007 年度神奈川大学総合理学研究所共同研究助成論