The domain of catalytic hydrogenation continues to grow fast, reflecting the wide range of chemical applications that can be enhanced by the easy use of molecular hydrogen. The advances in characterization techniques and their application have improved our understanding of the catalytic processes and mechanisms occurring in both homogeneous and heterogeneous catalysis.
Hemoglobin-oxygen dissociation curve. The hemoglobin tetramer can bind up to four molecules of oxygen in the iron-containing sites of the heme
molecules. As oxygen is bound, 2,3-BPG and CO2 are expelled. Salt bridges are broken, and each of the globin molecules changes its conformation to facilitate oxygen binding. Oxygen release to the tissues is the reverse process, salt bridges being formed and 2,3-BPG and CO2 bound. Deoxyhemoglobin does not bind oxygen efficiently until the cell returns to conditions of higher pH, the most important modulator of O2 affinity (Bohr effect).
Duckd2-crystallin is a soluble tetrameric lens protein. In
the presence of guanidinium hydrochloride (GdnHCl),it
undergoes stepwise dissociation and unfolding. Gel-filtra-tion chromatography and sedimentation velocity analysis
has demonstrated the dissociation of the tetramer protein to
a monomeric intermediate with a dissociation constant of
. Dimers were also detected during the dissociation