Lysozyme from eggs of the Dipterous Ceratitis capitata (Wiedeman) has been purified by ionexchange chromatography and gel filtration and its physicochemical properties have been investigated. This is the first insect lysozyme characterized so far and it exhibits some properties different to those described for other animal lysozymes.
Lysozyme from the insect eggs has a molecular weight of about 23200 and a sedimentation coefficient of 2.4 S. Molecular weight determination by sodium dodecylsulphate gel electrophoresis indicates that the molecule consists of a single polypeptide chain.
This lysozyme preparation shows notable stability at acidic pH values and lability at alkaline pH values. It shows a single optimum pH at about 6.5.
Chitinase/muramidase specific activity ratio is around 350 times higher for the insect lysozyme than for the hen egg‐white enzyme.
The amino acid composition shows the presence of one tryptophan residue per molecule of enzyme. This fact differentiates the lysozyme from insect eggs from other animal and plant lysozymes. From the amino acid composition, the absorption coefficient and the partial specific volume are calculated.
Glycine is the N‐terminal residue.
Hydrolysis of polyphosphoinositides by phosphodiesterase has been demonstrated to be involved in the control of cytosolic Ca2+ concentrations. The stimulation of Ca2+ ionophores of the release of inositol phosphates in macrophages, and other cells, together with the Ca2+ requirements for zymosan-induced phospholipase C activation, make unclear the relationship between Ca2+ mobilization and polyphosphoinositide hydrolysis. The results in the present paper strongly suggest that, for zymosan-induced phospholipase C activation, a previous increase in cytosolic Ca2+ is not a required event. These results also show that zymosan-activated release of inositol phosphates may be mediated by a guanine-nucleotide-binding protein.
The interaction between lipopolysaccharide from E. coli 0111:B4 and rat alveolar type II pneumocytes and its influence on the functional properties of the cells and their membranes were studied. Type II cells were isolated by a novel procedure involving digestion of the lung connective tissue with elastase and Percoll-gradient centrifugation. Binding of (14C)lipopolysaccharide to type II cells resulted in a partially reversible; non-specific, high affinity process. (14C)Choline incorporation into phosphatidylcholine by type II cells was stimulated by lipopolysaccharide, the maximum effect being observed at 10-20 micrograms/ml. 45Ca2+ uptake by type II cells was also increased by lipopolysaccharide. Using plasma membranes from lung homogenates an increase of membrane microviscosity versus the amount of lipopolysaccharide was shown. These results indicate that E. coli lipopolysaccharide interacts with alveolar type II cells by binding reversibly to particular ingredients of the membrane bilayer and induces a modification of ion permeability and fluidity of the membrane.
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