For investigation of the conformation of the unfolded species and its role in the refolding kinetics, refolding kinetic measurements were made on hen egg-white lysozyme by using the stopped-flow method at 25 degrees C in the four sets of initial and final folding condition: (1) 4 M guanidinium chloride (GdmCl) and 0.5 M GdmCl; (2) 40% acetic acid (HOAc) and 5% HOAc; (3) 4 M GdmCl and 0.5 M GdmCl-5% HOAc; (4) 40% HOAc and 0.5 M GdmCl-5% HOAc. The kinetic results as measured by absorbance at three wavelengths, 301, 292, 250 nm, agreed with each other and indicated strict biphasic behavior without exception. The kinetic parameters were determined only by the final refolding conditions. The spectral properties of the unfolded species at the end of stopped-flow mixing were investigated by comparing the total kinetic amplitude with the difference between the static absorbance of the native molecule in the final refolding conditions and that of the unfolded molecule in the initial unfolding conditions. The solvent effect was considered in the comparison. It was concluded that the unfolded species assumed a new transient conformation in the mixing process and that the transformation was completed within the mixing time.

Refolding kinetics of hen egg-white lysozyme (HEWL) have been studied by means of the stopped-flow method with guanidinium chloride as the denaturant. We show here that the three-species model U1 in equilibrium or formed from U2 in equilibrium or formed from N (U1 and U2 = unfolded; N = native) now established for pancreatic ribonuclease A is also valid for HEWL on the basis of the following lines of evidence: (1) refolding kinetics outside the transition region are biphasic; (2) dependence of the fractional amplitude for the fast phase on the ratio of the time constants of the two phases agrees with theory; (3) unfolding kinetics outside the transition region are of single phase; (4) direct evidence for the U2 leads to U1 transformation is obtained by double-jump experiments; (5) the time constant of the binding reaction of a substrate analogue, 4-methylumbelliferyl N,-N'-diacetyl-beta-chitobioside, to HEWL molecules during refolding reaction agrees with the time constant of the direct refolding phase U2 leads to N. The characteristic properties of the nucleation-controlled reaction of refolding of small globular proteins are discussed in general. The results of the discussion are used to suggest that the direct folding process is nucleation controlled from the experimental results of the temperature dependence of the refolding rate.

It is well known that inactivation of von Hippel-Lindau (VHL) gene predisposes for human clear cell renal carcinoma (CCRC). However, details about critical roles of VHL inactivation during tumorigenesis are still unknown. MET protein is a tyrosine kinase receptor for hepatocyte growth factor/ scatter factor (HGF/SF), which regulates cell growth, cell morphology, and cell motility. We showed that MET protein overexpressed in CCRC cells was phosphorylated without HGF/SF. This constitutive phosphorylation of MET protein in CCRC cells was inhibited by the rescue of exogenous wild-type VHL gene without a decrease in expression level of MET protein. Interestingly, wild-type VHL gene suppressed the phosphorylation of MET protein only under high cell density conditions. Additionally, MET protein activated by the inactivation of VHL gene modified cell adherence, including N-cadherin and B-catenin. When activation of MET protein in CCRC cells was inhibited by the MET inhibitor K252a, the growth of CCRC cells in vitro and the tumorigenesis induced by CCRC cells in nude mice were suppressed. From these results, we concluded that inactivation of VHL gene induced constitutive phosphorylation of MET protein and modified intercellular adherence structure to trigger the cell growth released from contact inhibition, finally resulting in tumorigenesis. This is one of the mechanisms of CCRC oncogenesis, and MET protein has potential as a molecular target for novel CCRC therapies. (Cancer Res 2006; 66(7): 3699-705)

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Quantum dots (QDs) are well known for their potential application in biosensing, ex vivo live-cell imaging and in vivo animal targeting. The brain is a challenging organ for drug delivery, because the blood brain barrier (BBB) functions as a gatekeeper guarding the body from exogenous substances. Here, we evaluated the distribution of bioconjugated QDs, i.e., captopril-conjugated QDs (QDs-cap) following intraperitoneal injection into male ICR mice as a model system for determining the tissue localization of QDs, employing ICP-MS and confocal microscopy coupled with spectrometric analysis. We have demonstrated that intraperitoneally administered QDs-cap were delivered via systemic blood circulation into liver, spleen, kidney and brain at 6 h after injection. QDs-cap were located predominantly inside the blood vessels in the liver, kidney and brain, but a few were distributed in the parenchyma, especially noteworthy in the brain. Careful studies on acute as well as chronic toxicity of QDs in the brain are required prior to clinical application to humans.