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881.
Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein. 相似文献
882.
Kinetics of RNA replication 总被引:4,自引:0,他引:4
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A method for the determination of the A-T content of DNA based on second-derivative ultraviolet spectra is presented. It allows measurement in a wide range of pH values, ionic strengths, and buffer media. It is nondestructive for the sample and requires not more than 10 micrograms of DNA. 相似文献
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Immunization of cancer patients with tumor-specific antigenic peptides is currently being tested in several clinical studies. We have examined the induction of CTL responses in mice after various modalities of peptide vaccination, to explore protocols that could be applied to humans. Our first model antigen was P198, which results from a point mutation in a normal gene. While two immunizations with peptide P198 in SBAS-1c adjuvant induced measurable CTL responses in less than 10% of DBA/2 mice, the addition of IL-12 to the peptide adjuvant mixture resulted in high CTL responses in nearly all mice. This strong enhancing effect of IL-12 was observed with 1,000 and 300 units and decreased gradually as the doses were reduced to 30 units. When IL-12 was replaced by other cytokines acting on T cells or antigen-presenting cells, such as IFN-gamma, IL-2, IL-6, IL-7, GM-CSF or MCP-3, no significant enhancing effect was observed. The same effect of IL-12 was obtained with peptide P1A, which is a major tumor-specific antigen of mastocytoma P815 and is encoded by a gene that is specifically activated in tumors. 相似文献