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At least 217 records · Page 12Linked to original sources
PubMed1972

Mercaptan-induced fragmentation of a subunit-like proteolytic fragment of immunoglobulin M.

Limited papain hydrolysis of immunoglobulin M (IgM) produces a subunit-like proteolytic fragment designated IgM(p) (Inman & Hazen, 1968). In the presence of mercaptans, IgM(p) partially dissociated into Fc(mu)-like and Fab(mu) fragments. Treatment of residual IgM (that remaining after a papain digestion) with 2mm-mercaptoethylamine resulted in fragmentation of the same type that occurs in a routine limited digestion of IgM with papain, although exogenous enzyme was not added to the mixture. When IgM was hydrolysed with (14)C-labelled papain, a small quantity of the enzyme was found to be associated with the residual IgM and IgM(p) fractions. IgM and IgM 7S subunit (IgM(s)) that had been exposed to papain in the absence of activating mercaptan and separated from the enzyme by gel filtration also fragmented when subsequently treated with 2mm-mercaptoethylamine. The fragments resembled those produced during a typical limited papain digestion of IgM. It was concluded that mercaptoethylamine induced fragmentation of IgM(p) by activating adsorbed papain.

Carbon Isotopes↗
PubMedDate not supplied

[Study of the conditions for the breakdown of mixed disulfides between aminothiol protectors and cell proteins as factors that determine the stability of the disulfide bonds].

A glutathione reductase activity was unaltered in thymus and liver tissue and slightly increased in spleen of rats within 15-30 min after administration of a radioprotector mercaptoethylamine. At the same time an activation of unspecific disulphide reductase occured. The both enzymes participated in spliting of mercaptoethylamine disulphides coupled with proteins. The radioprotective effectiveness of the aminothiol was, though partially, due to development of these disulfides. Retention of disulfides between the protector and cell proteins could be extended up to 1 h. by administration of mercaptoethylamine into rats with decreased content of endogenous glutathione, caused by the previous treatment with cyclohexene.

Animals↗
PubMed1975

Mechanism of immunoglobulin A polymerization.

Employing mercaptoethylamine as a reducing agent, it was demonstrated by analytical ultracentrifugation and polyacrylamide gel electrophoresis that polymeric immunoglobulin A (IgA) was reduced to a 10 S dimer and 7 S monomer, and that dimer IgA was more resistant to reductive cleavage than the higher polymers. When dimer and monomer IgA were subjected to electrophoresis in polyacrylamide gels in 8 M urea or chromatographed on Bio-Gel P-200 equilibrated in 4 M guanidine HCl, there was no dissociations into H, L, or J chains, suggesting that the interchain disulfide bridges between H--H, L--H, and H--J were intact and that mercaptoethylamine produced selective cleavage of intersubunit bonds. Only the dimer, with a sedimentation coefficient of 10.2 S, released J chain upon reduction with dithiothreitol. Polymers of IgA were reduced with mercaptoethylamine and subsequently alkylated with [14C]-iodoacetamide and the dimer and monomer isolated. The results demonstrated that the isolated dimer contained 2 mol of [14C]labeled S carboxyamidomethylcysteine per mol of dimer, while the monomer contained 1 mol of --SH per mol of monomer. The labeled dimer was then completely reduced with dithiothreitol and alkylated with [14C]iodoacetamide and J chain isolated. It was shown that the J chain contained no 14C-labeled sulfhydryl groups, while the monomer contained 1 mol of --SH per mol of monomer. These results suggest that J chain is disulfide-bonded to only two of the subunits of polymeric IgA and that the remaining subunits in the higher polymers are disulfide-bonded one to the other. This is similar to the model previously suggested for 19 S immunoglobulin M (IgM). The sulfhydryl data also suggests that polymeric IgA may not be a covalently bonded circular structure as has been shown for IgM. However, no conclusions can be made from this study regarding the structure of pentameric IgA, since this species was present in very small amounts in our polymer preparation.

Binding Sites↗
PubMedDate not supplied

[Effect of MEA on the degradation of thermally-damaged DNA in gamma-irradiated bacterial cells].

It was shown that the radioprotective action of beta-mercaptoethylamine on gamma-irradiated Bacillus stearothermophilus, with regard to survival and diminution of DNA breaks, depended upon the temperature of incubation and the presence of thermal lesions in DNA. beta-Mercaptoethylamine decreased the number of both alkali-labile sites and true single-strand DNA breaks in cells of Bacillus stearothermophilus. beta-Mercaptoethylamine decreased the number of alkali--labile sites and true single-strand breaks in DNA of Escherichia coli cells heated at 52 degrees C.

Cell Survival↗