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Biomedical subjects

A Barron

Publications and source records attributed to A Barron.

11 recordsLinked to original sources
PubMed1991

Capacity of CD8+ T cells to reject immunogenic variants of a spontaneous murine carcinoma: lack of non-specific (NK1.1+) effector mechanisms.

Class I MHC-expressing (Ia-) immunogenic (imm +) variants, which elicit a strong syngeneic host immune rejection response, can be isolated following 5-azacytidine treatment from the MHC-negative non-immunogenic (imm-) murine carcinoma cell line SP1 (10.1 subclone). In the present study, we have shown that CD4-depleted CD8+ T cells are both necessary and sufficient for the rejection process. Treatment of semi-syngeneic B6 X CBA F1 mice with anti-NK1.1 antibodies had no effect on the rejection of immunogenic variants, although the splenic NK (natural killer) activity of recipients was fully abrogated. Thus NK1.1+ effectors, which include most NK and LAK (lymphokine activated killer) cells, are most likely not involved in the rejection process. This finding was supported by a complete lack of NK susceptibility of SP1 cells in vitro, although variable killing by LAK and poly-I: C-induced killer cells was observed. To assess the role of NK1.1-LAK and other non-T killers (e.g. cytolytic macrophages) in vivo, we determined the specificity of the rejection process. We examined the ability of immune animals to reject a mixture of non-immunogenic parent tumour cells (or cells of an unrelated syngeneic tumour) and of the variant tumour cells used for the initial immunization. Growth of the parent tumour cells was unaffected while the same animals rejected the immunogenic tumour cells. Our findings support a primary role of tumour-specific CD8+ T cells in the rejection of imm+ variants with no detectable involvement of non-specific effector cells in the tumour destruction process.

Adenocarcinoma↗
PubMed1987

Purification and characterization of a glycine betaine binding protein from Escherichia coli.

A major component of the Escherichia coli response to elevated medium osmolarity is the synthesis of a periplasmic protein with an Mr of 31,000. The protein was absent in mutants with lambda placMu insertions in the proU region, a locus involved in transport of the osmoprotectant glycine betaine. This periplasmic protein has now been purified to homogeneity. Antibody directed against the purified periplasmic protein crossreacts with the fusion protein produced as a result of the lambda placMu insertion, indicating that proU is the structural gene specifying the 31-kDa protein. The purified protein binds glycine betaine with high affinity but has no affinity for either proline or choline, clarifying the role of proU in osmoprotectant transport. The amino-terminal sequence of the mature glycine betaine binding protein is Ala-Asp-Leu-Pro-Gly-Lys-Gly-Ile-Thr-Val-Asn-Pro.

Amino Acid Sequence↗
PubMed1986

Regulation of envelope protein composition during adaptation to osmotic stress in Escherichia coli.

Adaptation to osmotic stress alters the amounts of several specific proteins in the Escherichia coli K-12 envelope. The most striking feature of the response to elevated osmolarity was the strong induction of a periplasmic protein with an Mr of 31,000. This protein was absent in mutants with lambda plac Mu insertions in an osmotically inducible locus mapping near 58 min. The insertions are likely to be in proU, a locus encoding a transport activity for the osmoprotectants glycine betaine and proline. Factors affecting the extent of proU induction were identified by direct examination of periplasmic proteins on sodium dodecyl sulfate gels and by measuring beta-galactosidase activity from proU-lac fusions. Expression was stimulated by increasing additions of salt or sucrose to minimal medium, up to a maximum at 0.5 M NaCl. Exogenous glycine betaine acted as an osmoregulatory signal; its addition to the high-osmolarity medium substantially repressed the expression of the 31,000-dalton periplasmic protein and the proU-lac+ fusions. Elevated osmolarity also caused the appearance of a second periplasmic protein (Mr = 16,000), and severe reduction in the amounts of two others. In the outer membrane, the well-characterized repression of OmpF by high osmolarity was observed and was reversed by glycine betaine. Additional changes in membrane composition were also responsive to glycine betaine regulation.

Adaptation, Physiological↗
PubMed1985

Comparative stability and catalytic and chemical properties of the sulfate-activating enzymes from Penicillium chrysogenum (mesophile) and Penicillium duponti (thermophile).

ATP sulfurylases from Penicillium chrysogenum (a mesophile) and from Penicillium duponti (a thermophile) had a native molecular weight of about 440,000 and a subunit molecular weight of about 69,000. (The P. duponti subunit appeared to be a little smaller than the P. chrysogenum subunit.) The P. duponti enzyme was about 100 times more heat stable than the P. chrysogenum enzyme; k inact (the first-order rate constant for inactivation) at 65 degrees C = 3.3 X 10(-4) s-1 for P. duponti and 3.0 X 10(-2) s-1 for P. chrysogenum. The P. duponti enzyme was also more stable to low pH and urea at 30 degrees C. Rabbit serum antibodies to each enzyme showed heterologous cross-reaction. Amino acid analyses disclosed no major compositional differences between the two enzymes. The analogous Km and Ki values of the forward and reverse reactions were also essentially identical at 30 degrees C. At 30 degrees C, the physiologically important adenosine 5'-phosphosulfate (APS) synthesis activity of the P. duponti enzyme was 4 U mg of protein-1, which is about half that of the P. chrysogenum enzyme. The molybdolysis and ATP synthesis activities of the P. duponti enzyme at 30 degrees C were similar to those of the P. chrysogenum enzyme. At 50 degrees C, the APS synthesis activity of the P. duponti enzyme was 12 to 19 U mg of protein-1, which was higher than that of the P. chrysogenum enzyme at 30 degrees C (8 +/- 1 U mg of protein-1). Treatment of the P. chrysogenum enzyme with 5,5'-dithiobis(2-nitrobenzoate) (DTNB) at 30 degrees C under nondenaturing conditions modified one free sulfhydryl group per subunit. Vmax was not significantly altered, but the catalytic activity at low magnesium-ATP or SO4(2-) (or MoO4(2-)) was markedly reduced. Chemical modification with tetranitromethane had the same results on the kinetics. The native P. duponti enzyme was relatively unreactive toward DTNB or tetranitromethane at 30 degrees C and pH 8.0 or pH 9.0, but at 50 degrees C and pH 8.0, DTNB rapidly modified one SH group per subunit. APS kinase (the second sulfate-activating enzyme) of P. chrysogenum dissociated into inactive subunits at 42 degrees C. The P. duponti enzyme remained intact and active at 42 degrees C.

Amino Acids↗
PubMedDate not supplied

Nerve conduction studies in leprosy.

Motor and sensory nerve conduction studies have been performed on the peripheral nerves in the upper and lower limbs of 30 control subjects, and 36 subjects with leprosy from the Aboriginal population of the Northern Territory of Australia. Impairment of conduction was demonstrated in the vast majority of clinically abnormal nerves, and a large proportion of nerves which appeared clinically to be uninvolved. In a third group of subjects, abnormal conduction was demonstrated in a significant number of nerves which were considered to be clinically enlarged but in whom the diagnosis was initially in doubt. The majority of these patients were subsequently proven to have leprosy. It is concluded that nerve conduction studies are of considerable value in the diagnosis and management of leprosy.

Action Potentials↗