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S Chin

Publications and source records attributed to S Chin.

At least 91 records · Page 5Linked to original sources
PubMed1985

Interaction of K+ ion with the solvated gramicidin A transmembrane channel.

Using Urry's gramicidin A (GA) atomic coordinates and ab into calculations, the interaction energies of a K+ ion with GA are examined. From these energies the values of the fitting parameters are obtained for 6-12-1 atom-atom pair potentials. The potential of the GA channel as experienced by the ion is analyzed in detail. An energy profile of the K+ ion in the GA channel is obtained by analyzing iso-energy maps. Using Monte Carlo simulations, the energy profiles of the K+ ion with the solvated GA channel are analyzed and the hydration structures in the presence of the K+ ion are studied.

Gramicidin↗
PubMed1985

A new assay for fibronectin opsonic activity and its application to plasma and plasma fractions.

A homologous assay system for human plasma fibronectin opsonic activity is presented. The system utilizes peripheral leukocytes purified from leukocyte concentrates and a metabolizable, radiolabeled lipid emulsion which has been gelatin-coated. The uptake of radiolabeled lipid was shown to depend on the presence of fibronectin and was stimulated by the addition of heparin. Both polymorphonuclear leukocytes (PMNs) and monocytes were active in this system. That at least a portion of the incorporated radiolabeled lipid emulsion was phagocytosed was indicated through the use of metabolic inhibitors, trypsin, and direct electron microscopic observation. This assay was applied to the analysis of donor plasma and plasma fractions. Opsonic activity levels measured with this assay system were shown to correlate (p = 0.05) with the level of fibronectin antigen in 17 samples of dialyzed normal donor plasma. Fibronectin opsonic activity was retained by outdated liquid plasma, cryo-depleted plasma, and cryoprecipitate; however, Cohn fraction I appeared to lose considerable fibronectin opsonic activity relative to fibronectin antigen.

Biological Assay↗
PubMed1981

Tumor promoters alter gene expression and protein phosphorylation in avian cells in culture.

We have investigated the effect of 12-O-tetradecanoylphorbol 13-acetate (TPA) on the synthesis and modification of polypeptides in normal avian cells and cells infected by wild-type and temperature-sensitive Rous sarcoma virus (RSV). Using two-dimensional gel electrophoresis, we have detected alterations in both the abundance of cellular polypeptides and in their phosphorylation that seem unique to TPA treatment. However, the state of phosphorylation of the major putative substrate for the action of the src gene-associated protein kinase, the 34- to 36-kilodalton protein, was not altered. Moreover, examination of the phosphorylated amino acid content of total cellular phosphoproteins revealed that the response to TPA was not associated with detectable increases in their phosphotyrosine content. These results make it unlikely that TPA acts by the activation of the phosphorylating activity of the cellular proto-src gene or by the activation of other cellular phosphotyrosine-specific kinases. We have shown previously that temperature-sensitive RSV-infected cells at nonpermissive temperature demonstrate an increased sensitivity to TPA treatment [Bissell, M. J., Hatie, C. & Calvin, M. (1979) Proc. Natl. Acad. Sci. USA 76, 348-352]. Our present results indicate that this is not due to reactivation of the phosphorylating activity of the defective src gene product or to its leakiness, and they lend support to the notion of multistep viral carcinogenesis.

Animals↗