Cell membranes lysozyme

A potentiometric determination of lysozyme is based on a system similar to a bacterial electrode [11]. The cells of the bacteria, Mcrococcus lysodeicticus, readily accept trimethylphenyl ammonium ions (TMPA ) from the solution. Lysozyme decomposes the cell membranes and TMPA is liberated. The rate... 

The teichoic acids of the wall and membrane act as a buffer system maintaining a concentration of Mg2 in the range of 10-15 mM, which is the optimum value for the activity of enzymes associated with membranes 31). Changes of the Mg2 + concentration in the medium have no effect on the activity of membrane-bound enzymes if the system keeps both the membrane and the cell wall closely in contact. Preparations devoid of cell walls (lysozyme digestion) exhibit a dependence of enzyme activity on the Mg2 + concentration. The membrane fragments without LTAs show a marked influence of the Mg2+ concentration on enzyme activity 31). 

Ion channels are found not only in the cell membrane but also in the membranes of the intracellular organelles such as mitochondria, lysozymes, nucleus, and secretory, endocytotic, and synaptic vesicles, as well as in the endoplasmic/sacroplasmic reticulum (ER/SR). Two major intracellular Ca channels, the inositol 1,4,5-trisphosphate (IP3) receptor and the ryanodine receptor (RyR), are located in the ER/SR membranes and contribute to changes in intracellular Ca concentration. Based on their mechanism of activation, these two channels are classified as ligand-gated channels (Section 16.4.1). 

John C. Kendrew determined the first atomic-scale (2A resolution) crystallographic structure of a protein, myoglobin (molecular mass 16,900 Da or 16.9 KDa) in 1959 and Max Perutz followed shortly afterward with atomic scale resolution of the tetrameric protein hemoglobin (64,500 Da). The first crystallographic structure for an enzyme, lysozyme (13,900 Da), was determined by David Phillips in 1965. The crystallographic analysis of the structure of the supermolecular photosynthetic reaction center of purple photosynthetic bacteria in 1985 led to a Nobel Prize in chemistry for Robert Huber, Johann Diesenhofer, and Hartmut Michel. The reaction center, a complete nanomachine embedded in the cell membrane of purple photosynthetic bacteria, consists of 4 protein subunits and 14 cofactors. 

Localization of a-D-galactosidase in an alkalophilic strain of Micrococcus was investigated in relation to the cell membrane as a permeability barrier. The a-D-galactosidase appeared to be mostly intracellular only about 4% of a-D-galactosidase was released by lysozyme or freeze-thaw treatments of the whole cells. The enzyme activity was not inhibited by treatment of the whole cells with diazo-7-amino-l,3-naphthalene disulphonic acid, which penetrated the cell wall but not the cytoplasmic membrane. The enzyme activity of the whole cells increased about four-fold by toluene-acetone treatment which caused an alteration in the membrane permeability. The enzyme in such cells became to be relatively sensitive to pH. These results showed that cell membrane played a protective role as a permeability barrier against alkaline environment. 

Lysozyme brings about hydrolysis of the bacterial cell wall, specifically, the P-1, 4-glycosidic bonds. Activity toward gram-negative species is limited because of the protective outer cell membrane in this group (Villa, 1996). Lysozyme has no effect on yeasts. 

The inner cell wall, like that of bacteria, consists of murein anchored in the cell membrane. It is attacked by lysozyme. Outside the murein layer is a plasmatic layer, and beyond that there may be a slime capside. 

The complex outer layers beyond the peptidoglycan in the Gram-negative species, the outer membrane, protect the organism to a certain extent from the action of toxic chemicals (see Chapter 13). Thus, disinfectants are often effective only at concentrations higher than those affecting Gram-positive cells and these layers provide unique protection to the cells from the action of benzylpenicillin and lysozyme. 

To check if PemB is surface exposed, E. chrysanthemi cells were subjected to proteolysis. Treatment of the cell suspension with trypsin, proteinase K or chimotrypsin at a concentration of 0.1 to 1 mg/ml for 1 h did not cause PemB proteolysis or its liberation into the medium. Cell pre-treatment with EDTA-lysozyme, which renders the periplasmic proteins accessible to proteases, gave no effect. PemB was also resistant to proteolytic digestion in extract of cells disrupted by sonication or in a French press. Only addition of Triton X-100 (up to 0.1%) causing formation of the micelles with PemB lead to a quick proteolyis of this protein (data not shown). In another approach to analyse the PemB exposition, bacterial cells were labelled with sulfo-NHS-biotin. This compound is unable to cross membranes and biotinylation... 

Patients with thermal injury are also deficient in specific granules. In this case, however, it appears that this deficit is due to activation of the cells such that they discharge their specific granules. Neutrophils from patients with bums have an increased expression of plasma-membrane markers (as would be predicted if specific-granule membranes have fused with the plasma membrane), and serum levels of lysozyme and lactoferrin are elevated. These patients have impaired chemotaxis and defective oxygen metabolism. 

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