PubMed · 228977
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W Bors, C Michel, M Saran. 1979-11-15. Superoxide anions do not react with hydroperoxides.. https://doi.org/10.1016/0014-5793(79)80417-2
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The motion of single, dye-labeled protein molecules was monitored at various pH and ionic strengths within the 180-nanometer-thick evanescent-field layer at a fused-silica surface. Below the isoelectric point, molecules partitioning into the excitation region increased in number but maintained a random spatial distribution, implying that surface charge can influence the charged protein at distances beyond that of the electrical double-layer thickness. The residence times of the molecules in the interfacial layer also increased below the isoelectric point. However, immobilization on the solid surface for extended periods was not observed. Histograms of residence times exhibit nearly identical asymmetry as the corresponding elution peaks in capillary electrophoresis. These results are a direct verification of the statistical theory of chromatography at the single-molecule level, with the caveat that long-range trapping rather than adsorption is the dominant mechanism.
The similarities and differences in retention characteristics of aromatic and aliphatic phases have been elucidated by the use of linear solvation energy relationships (LSERs). Three aromatic phases and three aliphatic phases were investigated in a series of mobile phases. The results of LSERs on a polymer-based aromatic phase, poly(styrene-divinylbenzene) resin (PRP-1) are very different from those on either silica- or zirconia-based aromatic and aliphatic phases. Retention on all aromatic and aliphatic phases except PRP-1 is dominated by two factors: the solute size and hydrogen bond acceptor basicity. On the other hand, in addition to these two major contributions, retention on PRP-1 is markedly influenced by the solute hydrogen bond donor acidity. We believe that PRP-1 exhibits a more adsorption-like retention mechanism than do the other phases. With the inorganic oxide-based phases, the aromatic phases are less retentive than the aliphatic phases but show a larger dependence on molecular polarizability. The enhanced polarizability of aromatic phases is the likely cause of some differences in their chromatographic selectivity relative to the aliphatic phases.
We have used citrate synthase from Thermoplasma (Tp.) acidophilum as a thermostable model system to investigate the role of hydrophobic interactions in dimer interface for maintaining high temperature stability. Three mutant enzymes were constructed by single amino acid substitutions in the interface helices: Ala97-->Ser, Ala104-->Thr, and Gly209-->Ala. All of the mutations enhanced the thermostability of Tp. citrate synthase, while improving its catalytic properties (Km, Vmax, and specific activity). The highest thermostability was achieved by the Gly209-->Ala substitution. The half-life of irreversible inactivation of the G209A mutant enzyme at 85 degreesC was about 57 min, and the midpoint of guanidinium chloride (GdmCl) induced irreversible denaturation was at 2.0 M GdmCl. Our results showed that amino acid substitutions increasing or decreasing interface hydrophobicity could further increase the thermostability of the Tp. citrate synthase. Thus, interface substitutions affecting the entropy of the unfolded state did not prove to be so critical in protein thermostabilization at higher temperatures.