Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.17 (lysozyme)
21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. A cell-free preparation of membrane fragments was prepared from the thermophilic blue-green alga Phormidium laminosum by lysozyme treatment of the cells followed by osmotic shock to lyse the spheroplasts. The membrane fragments showed high rates of photosynthetic electron transport and O2 evolution (180-250 mumol of O2/h per mg of chlorophyll a with 2,6-dimethyl-1,4-benzoquinone as electron acceptor). O2-evolution activity was stable provided that cations (e.g. 10mM-Mg2+ or 100mM-Na+) or glycerol (25%, v/v) were present in the suspending medium. 2. The components of the electron-transport chain in P. laminosum were similar to those of other blue-green algae: the cells contained Pigment P700, plastocyanin, soluble high-potential cytochrome c-553, soluble low-potential cytochrome c-54 and membrane-bound cytochromes f, b-563 and b-559 (both low- and high-potential forms). The amounts and midpoint potentials of the membrane-bound cytochromes were similar to those in higher-plant chloroplasts. 3. Although O2 evolution in P. laminosum spheroplasts was resistant to high temperatures, thermal stability was not retained in the cell-free preparation. However, in contrast with higher plants, O2 evolution in P. laminosum membrane fragments was remarkably resistant to the non-ionic detergent Triton X-100.
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PMID:Photosynthetic electron transport in a cell-free preparation from the thermophilic blue-green alga Phormidium laminosum. 677 63

Clostridium pasteurianum is able to build up about 100-fold gradients of methylammonium across the cell membrane. Methylammonium enters the cell by means of a carrier as shown by the energy requirement, saturation kinetics and a pH profile with a narrow maximum between pH 6.2 and 6.8. The methyl ammonium transport (apparent Km = 150 microM, V = 100 mumol/min per g dry weight) is competitively inhibited by ammonium (apparent Ki = 9 microM). The low Ki value and the observation that methylammonium cannot serve as a carbon or nitrogen source for Cl. pasteurianum strongly indicate that ammonium rather than methylammonium is the natural substrate. Uncouplers and inhibitors of energy metabolism or of the membrane-bound ATPase inhibit transport. Cl. pasteurianum maintains a membrane potential (interior negative) in the range 80-130 mV. This membrane potential was identified as the energy source: the same agents that block transport also decrease the membrane potential, and artificial generation of a membrane potential (by addition of valinomycin to K+-loaded cells) induces concentrative uptake of methylammonium. Thus NH4+ (or CH3NH3+) must be the transported species. Digestion of the cell wall by lysozyme does not abolish the transport activity.
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PMID:Some properties of a new electrogenic transport system: the ammonium (methylammonium) carrier from Clostridium pasteurianum. 721 10

Various dehydrogenases, reductases, and electron transfer proteins involved in respiratory sulfate reduction by Desulfovibrio gigas have been localized with respect to the periplasmic space, membrane, and cytoplasm. This species was grown on a lactate-sulfate medium, and the distribution of enzyme activities and concentrations of electron transfer components were determined in intact cells, cell fractions prepared with a French press, and lysozyme spheroplasts. A significant fraction of formate dehydrogenase was demonstrated to be localized in the periplasmic space in addition to hydrogenase and some c-type cytochrome. Cytochrome b, menaquinone, fumarate reductase, and nitrite reductase were largely localized on the cytoplasmic membrane. Fumarate reductase was situated on the inner aspect on the membrane, and the nitrite reductase appeared to be transmembraneous. Adenylylsulfate reductase, bisulfite reductase (desulfoviridin), pyruvate dehydrogenase, and succinate dehydrogenase activities were localized in the cytoplasm. Significant amounts of hydrogenase and c-type cytochromes were also detected in the cytoplasm. Growth of D. gigas on a formate-sulfate medium containing acetate resulted in a 10-fold increase in membrane-bound formate dehydrogenase and a doubling of c-type cytochromes. Growth on fumarate with formate resulted in an additional increase in b-type cytochrome compared with lactate-sulfate-grown cells.
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PMID:Localization of dehydrogenases, reductases, and electron transfer components in the sulfate-reducing bacterium Desulfovibrio gigas. 724 92

The kinetics of potentially autoreactive B-cells were investigated in a double-transgenic model of self-tolerance. Two types of transgenic mice were created for this purpose. In the first the great majority of B-cells expressed the rearranged heavy and light chain genes encoding a high affinity receptor for hen egg lysozyme (HEL), while the second type expressed HEL in either soluble (sHEL) or membrane-bound (mHEL) form. Double-transgenic (Dbl-Tg) mice were produced either by mating the two types of founders or by transferring bone marrow cells from Ig-transgenic (Ig-Tg) donors into irradiated HEL-Tg recipients. The lifespan of B-cells from the Dbl-Tg mice was measured by oral loading with the thymidine analogue, 5-bromo-2'-deoxyuridine (BrdU) for periods varying from three days to six weeks. Experiments in various combinations of Dbl-Tg mice revealed a three-tiered hierarchy of B-cell unresponsiveness, each level of which was characterised by a different B-cell lifespan. Exposure to mHEL led to rapid deletion of B-cells at an immature stage in their development with a median lifespan of approximately 15 hours. B-cells exposed to sHEL above a critical tolerogenic threshold were not deleted in the bone marrow but migrated to the spleen in an anergic state where they died within three days. If the receptor occupancy of sHEL was below the tolerogenic threshold, B-cells were neither deleted nor rendered anergic (ie were "indifferent") and had a normal median lifespan of four to five weeks.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Whither the anergic B-cell? 777 3

A gamma-glutamyl peptide-hydrolysing enzyme was partially purified from Actinobacillus actinomycetemcomitans. The enzyme required metal ions, and 1 to 2 mM Mn2+ ions, especially, were essential for hydrolytic reaction. Its distribution by treatment of cells with lysozyme-EDTA suggested that the enzyme was a membrane-bound protein. The pI of the enzyme was in range of pH 5.1 to 5.6, and the apparent Km value for gamma-glutamyl-p-nitroanilide was 3.0 x 10(-4) M. The enzyme hydrolysed specifically gamma-glutamyl residues from the N-terminal of gamma-glutamyl compounds such as gamma-Glu-Met, gamma-Glu-Ala, gamma-Glu-Leu and gamma-Glu-Tyr, but did not catalyse the transpeptidation reaction. Neither free amino acids such as Ala-, Pro-, Gly- and Leu-p-nitroanilide nor alpha-glutamyl derivatives were hydrolysed. Its activity was strongly inactivated by metal chelators (EDTA or o-phenanthroline) and amino acids (Glu, Gln). In addition, the activity was specifically inactivated by gamma-glutamyl affinity-labelling reagents such as AT-125, 6-diazo-5-oxo-L-norleucine and azaserine, which are inhibitors of the gamma-glutamyl donor sites of mammalian gamma-glutamyl transpeptidase. Antibodies against bovine kidney gamma-glutamyl transpeptidase decreased the activity of the bacterial enzyme by 65%. These results suggested that the active sites in the bacterial enzyme were similar to those in mammalian gamma-glutamyl transpeptidase.
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PMID:Partial purification and some properties of gamma-glutamyl peptide-hydrolysing enzyme from Actinobacillus actinomycetemcomitans. 779 32

Transgenic mice carrying a rearranged Ig gene encoding the H chain of a lysozyme-specific antibody were used to examine the effect of antigen binding affinity on elimination of self-reactive B cells. In H chain transgenic mice, B cells expressed surface IgM and IgD composed of lysozyme-specific H chains and many different possible L chains from endogenous L chain genes. Immunofluorescent staining and flow cytometry revealed a distinct subset comprising approximately 1% of spleen B cells that bound lysozyme with a high affinity comparable with the original lysozyme-specific antibody. Additional subsets accounting for a total of 5-6% of spleen B cells bound lysozyme more weakly, with the weakest requiring 10,000-fold higher concentrations of monomeric hen egg lysozyme to attain 50% receptor saturation. When the various B cell subpopulations were allowed to develop in animals expressing lysozyme as a membrane-bound antigen on autologous cells, both low and high affinity lysozyme-binding B cells were undetectable in peripheral lymphoid organs. These findings demonstrate the efficacy with which low affinity self-reactive B cells can be eliminated in vivo, consistent with the notion that this cellular mechanism accounts for the absence of natural IgM antibodies against self antigens on the surface of blood cells. The data also illustrate the potential use of Ig transgenic mice for analyzing and selecting novel receptor-ligand interactions.
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PMID:Censoring of self-reactive B cells with a range of receptor affinities in transgenic mice expressing heavy chains for a lysozyme-specific antibody. 781 51

Mice homozygous for the lymphoproliferation (lpr) mutation, which disrupts expression of the Fas cell surface molecule, develop an autoimmune syndrome with a spectrum of autoantibodies resembling human SLE. It is not known how the loss of Fas leads to autoantibody production. To study the fate of autoreactive B cells in lpr/lpr mice, C57BL/6 (B6) strain transgenic mice expressing hen egg lysozyme (HEL) as a model autoantigen in soluble or membrane-bound forms and carrying HEL-specific Ig (Ig) transgenes were mated onto the congenic B6-lpr/lpr background. Despite the absence of Fas, elimination of self-reactive lpr/lpr B cells recognizing membrane-bound autoantigen occurred as efficiently as in autoreactive B cells bearing the wild-type (+/+) Fas gene. Functional inactivation of autoreactive B cells binding soluble HEL also occurred normally in most young lpr/lpr animals. Nevertheless, breakdown of B cell tolerance to soluble lysozyme occurred in one of eight young lpr/lpr animals and in four of seven old animals with lymphadenopathy. Interestingly, the presence of the rearranged Ig transgenes markedly delayed the onset of lymphadenopathy. These results demonstrate that Fas is not an essential molecule in the biochemical pathways mediating autoreactive B cell elimination or inactivation. The breakdown of tolerance observed in a considerable fraction of older animals nevertheless confirms that autoantibody production in this model of SLE involves a defect in active censoring of autoreactive B cells. The possible basis for that defect is discussed.
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PMID:Effects of the lpr mutation on elimination and inactivation of self-reactive B cells. 807 85

A hydrophilic enzyme, lysozyme, was myristoylated in vitro by the N-hydroxysuccinimide ester of myristic acid and three monomyristoylated lysozymes modified at a distinct position (at Lys-13, Lys-33, Lys-97) were isolated by two-step column chromatography. The relationship between membrane binding and phosphorylation by protein kinase C of these monomyristoylated lysozymes were examined using phospholipid vesicles. These three lysozymes bound to phospholipid vesicles to the same extent, whereas the binding of nonmyristoylated native lysozyme was negligible. When native and three monomyristoylated lysozymes were reacted with protein kinase C in a phosphatidylserine (PS)-containing vesicle system, phosphorylation was observed with the myristoylated lysozymes, whereas that of native lysozyme was negligible. However, a remarkable (more than sixfold) difference in the extent of phosphorylation by protein kinase C was observed among three monomyristoylated lysozymes with a different myristoylated position. These results suggest that the membrane binding of substrate protein is not sufficient for the phosphorylation by protein kinase C and the topology of the substrate protein on the membrane play a crucial role in the recognition of substrate protein by protein kinase C. These results further indicate that protein myristoylation can modulate the topology of the membrane-bound protein.
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PMID:Myristoylation of protein at a distinct position allows its phosphorylation by protein kinase C. 808 Feb 81

To study the role of the B cell Ag receptor (membrane-bound Ig [mIg]) in Ag processing and presentation, we have generated several Ig transfectants that express transfected TEPC-15 idiotype (T15-Id) mIgM with phosphorylcholine (PC)-binding specificity. The wild-type Ig transfectant is able to present a specific Ag (e.g., PC-conjugated hen egg-white lysozyme [PC-HEL]) more efficiently than a nonspecific Ag (HEL) to a T cell hybridoma recognizing an epitope on the HEL molecule. A substitution in the entire spacer, transmembrane, and cytoplasmic region of mIg with an equivalent region of I-A alpha chain completely abolishes this mIg-enhanced Ag presentation. Experiments with the wild-type and substituted variant Ig transfectants suggest that this substitution may interfere with normal intracellular trafficking of mIg after cross-linking with specific Ag or antibodies specific for the mIg (anti-T15-Id mAb). Prolonged treatment of the wild-type Ig transfectants with specific Ag or anti-T15-Id mAb reduces the surface expression of T15-Id mIgM and leads to an accumulation of T15-Id mIgM inside the cells. The reduced surface expression and the elevated cytoplasmic accumulation of T15-Id mIgM are not observed in the variant Ig transfectant. Despite the ability of the variant to endocytose ligands similarly to the wild-type Ig transfectant, this variant displays a higher rate of recycling of the mIg/ligand complexes back to the cell surface and a lower rate of degradation of the ligands. These abnormalities may be responsible for the deficiency in mIg-mediated enhancement of Ag presentation in the variant Ig transfectant. Therefore, our results suggest that the transmembrane region of mIg is involved in intracellular trafficking of receptor/ligand complexes and that proper delivery and handling of internalized Ag are required for the enhanced presentation of specific Ag by B cells.
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PMID:Role of the B cell antigen receptor in antigen processing and presentation. Involvement of the transmembrane region in intracellular trafficking of receptor/ligand complexes. 824 57

The specificity of antibody (Ab) responses depends on focusing helper T (Th) lymphocyte signals to suitable B lymphocytes capable of binding foreign antigens (Ags), and away from nonspecific or self-reactive B cells. To investigate the molecular mechanisms that prevent the activation of self-reactive B lymphocytes, the activation requirements of B cells specific for the Ag hen egg lysozyme (HEL) obtained from immunoglobulin (Ig)-transgenic mice were compared with those of functionally tolerant B cells isolated from Ig-transgenic mice which also express soluble HEL. To eliminate the need for surface (s)Ig-mediated Ag uptake and presentation and allow the effects of sIg signaling to be studied in isolation, we assessed the ability of allogeneic T cells from bm12 strain mice to provide in vivo help to C57BL/6 strain-transgenic B cells. Interestingly, non-tolerant Ig-transgenic B cells required both allogeneic Th cells and binding of soluble HEL for efficient activation and Ab production. By contrast, tolerant self-reactive B cells from Ig/HEL double transgenic mice responded poorly to the same combination of allogeneic T cells and soluble HEL. The tolerant B cells were nevertheless normally responsive to stimulation with interleukin 4 and anti-CD40 Abs in vitro, suggesting that they retained the capacity to respond to mediators of T cell help. However, the tolerant B cells exhibited a proximal block in the sIg signaling pathway which prevented activation of receptor-associated tyrosine kinases in response to the binding of soluble HEL. The functional significance of this sIg signaling defect was confirmed by using a more potent membrane-bound form of HEL capable of triggering sIg signaling in tolerant B cells, which markedly restored their ability to collaborate with allogeneic Th cells and produce Ab. These findings indicate that Ag-specific B cells require two signals for mounting a T cell-dependent Ab response and identify regulation of sIg signaling as a mechanism for controlling self-reactive B cells.
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PMID:Immunoglobulin signal transduction guides the specificity of B cell-T cell interactions and is blocked in tolerant self-reactive B cells. 829 58


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