The solution behavior of lysozyme was studied as a function of protein concentration, NaCl concentration, pH, and temperature using pulsed-gradient spin-echo NMR diffusion measurements. The lysozyme solutions clearly exhibited nonideal behavior which was sensitive to both the salt concentration and pH. Lysozyme has an isoelectric point of pH 11, and it is often overlooked that at normal pH it has a net positive charge. Since lysozyme is a charged species, the changes in the diffusion coefficients were interpreted, considering the competing effects of salt-mediated changes in protein interactions (e.g., electrostatic repulsion) and aggregation. The behavior is in agreement with Derjaguin-Landau-Verwey-Overbeek (DLVO)-type modeling, accounting for the attractive and repulsive forces present. The diffusion data was compared with various self-association models, including corrections for the effects of self-obstruction. The diffusion coefficients of the higher oligomers were calculated, assuming that the monomers aggregated as hard spheres. Using an isodesmic association model, the equilibrium constant for the self-association of lysozyme at pH 4.6 and 298 K in the presence of 0.5 M NaCl was estimated to be 118 ( 12 M -1 .

Hop-derived aroma characteristics in beer are very important for the quality of beer. This study compared the differences of hop aroma characteristics and the compounds contained in beer by changing the variety of hops applying the idea of "food metabolomics" on the GC×GC/TOF-MS analysis data, to clarify which aroma compounds contribute to the differences of hop aroma profiles indicated by sensory descriptors. As a result, by focusing only on hop-derived compounds, 67 compounds were strongly correlated with one or more of the sensory descriptors. Furthermore, the odor descriptions of each key compound corresponded well to each sensory descriptor. Thus, these compounds are likely to be the key compounds explaining the differences of hop aroma characteristics in beer. This study led to the suggestion that understanding the relationship between the comprehensive nontarget analysis by GC×GC-TOF/MS and organoleptic evaluation using PCA is effective in estimating the key compounds.

The time dependence of aggregation in supersaturated lysozyme solutions was studied using pulsed-gradient spin-echo NMR diffusion measurements as a function of lysozyme concentration at pH 6.0 and 298 K in the presence of 0.5 M NaCl. The measurements provide estimates of the weight-averaged diffusion coefficient of the monomeric to intermediate molecular weight lysozyme species present in the solution (very large aggregates and crystals are excluded from the average due to the NMR relaxation-weighting effects inherent in the method). The results show that the average molecular weight of the various lysozyme aggregates changed with sigmoidal kinetics and that these kinetics were strongly influenced by the initial lysozyme concentration. The visualization of the time dependence of the protein aggregation afforded by this method provides a deeper understanding of how the crystallizing conditions (especially the initial protein concentration) are related to the resulting crystals.

The two killer toxins, SMK and KP4, share a unique folding topology which contains a rare structural motif. This observation may suggest that these toxins are evolutionally and/or functionally related. The pH-dependent stability of the SMK toxin is a result of the intensive interactions between the carboxyl groups. This finding is important for protein engineering, for instance, towards stabilization of the toxin molecule in a broader pH range. The present crystallographic study revealed that the structure of the SMK toxin itself is hardly affected by the ionic strength, implying that a high salt concentration affects the sensitivity of the cell against the toxin.

Medium-chain fatty acids (MCFAs) and ethyl esters are considered to contribute to some organoleptic properties, such as fatty odor and bitterness in Japanese sake. However, the relationships between these compounds and the organoleptic properties of sake remain unclear. Here, we quantified MCFAs and ethyl hexanoate in ginjo sake using gas chromatography with a flame ionization detector (GC-FID). The hexanoic acid concentration strongly correlated with fatty odor (p < 0.0001). The octanoic acid/hexanoic acid ratio correlated with butanoic acid concentration, which is likely correlated with inharmonious bitter taste. Multiple comparison analysis revealed that the ethyl hexanoate level was negatively correlated with bitterness. We then identified other chemical compounds correlating with fatty odor and bitterness using comprehensive two-dimensional GC coupled with time-of-flight mass spectrometry. By performing correlation analysis between certain compounds and sensory values following statistical selection for chemical compounds, we identified several candidate compounds correlating with fatty odor and bitterness in sake.