Proteins that encounter unfavorable solvent conditions are prone to aggregation, a phenomenon that remains poorly understood. This work focuses on myoglobin (Mb) as a model protein. Upon heating, Mb produces amorphous aggregates. Thermal unfolding experiments at low concentration (where aggregation is negligible), along with centrifugation assays, imply that Mb aggregation proceeds via globally unfolded conformers. This contrasts studies on other proteins that emphasized the role of partially folded structures as aggregate precursors. Molecular dynamics (MD) simulations were performed to gain insights into the mechanism by which heat-unfolded Mb molecules associate with one another. A prerequisite for these simulations was the development of a method for generating monomeric starting structures. Periodic boundary condition artifacts necessitated the implementation of a partially immobilized water layer lining the walls of the simulation box. Aggregation simulations were performed at 370 K to track the assembly of monomeric Mb into pentameric species. Binding events were preceded by multiple unsuccessful encounters. Even after association, protein−protein contacts remained in flux. Binding was mediated by hydrophobic contacts, along with salt bridges that involved hydrophobically embedded Lys residues. Overall, this work illustrates that atomistic MD simulations are well suited for garnering insights into protein aggregation mechanisms.

The spent sulphite liquor derived from Abitibi Paper Company, Iroquois Falls Mills Arbiso process contained about 11.3% dissolved solid, 0.52% (W/V) residual SO2 and had a low pH of 4.3. The COD of the liquor was about 109,000 ppm and BOD5 26,000 ppm. The objective of the study was to investigate the technical feasibility of utilizing biodegradation to reduce the BOD5 of the spent liquor to acceptable levels. Upon first analysis, it appeared that the liquor would be amenable to biological degradation because of the presence of wood sugars. However, biological oxidation was retarded due to the presence of SO2. The maximum SO2 concentration tolerated by the microbes was about 0.32% (W/V). Boiling and lime treatment were found to be effective in reducing the SO2. Other major factors affecting biological activity were initial pH adjustment and nutrient addition. Nutrients required and optimal operating conditions are discussed. Under optimal conditions, a batch biological system was capable of removing 60% BOD5, in 11 days and 80% BOD5 in 16 days.