Changes in the lipoproteins of human blood serum during processing.

Since 1939 the value of readily available whole blood, plasma and serum has received widespread and deserved recognition. For most purposes whole blood may be considered the ideal material for replacing lost blood, yet certain conditions, such as burns, in which hemoconcentration is to be combatted, call primarily for replacement of circulating fluid. In such cases plasma or serum may be the materials of choice. The chief advantage of plasma and serum, however, lies in their stability over long periods which makes possible the accumulation of large stores without wastage. The problem of maintaining such plasma or serum in the best possible condition for long periods of time thus assumes considerable importance.[...

Access of ligands to cavities within the core of a protein is rapid.

We have investigated the magnitude and timescale of fluctuations within the core of a protein using the exchange kinetics of indole and benzene binding to engineered hydrophobic cavities in T4 lysozyme. The crystal structures of variant-benzene complexes suggest that relatively large scale fluctuations (1-2 angstrom) of backbone atoms are required for entry of these ligands into the core. Nonetheless, these ligands enter the cavities rapidly, with bimolecular rate constants of approximately 10(6)-10(7) M(-1) s(-1) and a low activation barrier, 2-5 kcal mol(-1). These results suggest that protein cores undergo substantial fluctuations on the millisecond to microsecond timescale and that entry of small molecules into protein interiors is not strongly limited by steric occlusion