Association of the CD59 and CD55 cell surface glycoproteins with other membrane molecules.

mAb against human glycosyl-phosphatidylinositol-linked leucocyte surface Ag CD59 and CD55 immunoprecipitated from detergent lysates of HPB ALL cell line in addition to the respective Ag a common 80-kDa glycoprotein component and (glyco)lipids. The 80-kDa glycoprotein is different from otherwise similar CD44 Ag. The CD59 immunoprecipitate contained also a small amount of the CD55 glycoprotein and the CD55 immunoprecipitate minute amount of the CD59 Ag. These results are interpreted in terms of existence of noncovalent complexes resistant to dissociation by mild detergents and consisting of the 80-kDa glycoprotein, CD59 and CD55 glycoproteins, relatively tightly bound (glyco)lipids and possibly other so far unidentified components. These complexes contain probably also other glycosyl-phosphatidylinositol-linked Ag, as an anti-CD48 mAb immunoprecipitated also an apparently very similar complex. The complexes immunoprecipitated by mAb against the CD55, CD59, and CD48 Ag also contain a protein kinase activity. This type of complexes could not be demonstrated in several other cell types such as RBC, PBMC, and HeLa cells. However, a qualitatively very similar set of components was immunoprecipitated from the murine thymoma EL-4 cell line by an anti-Thy-1 mAb.     

Purification, characterization, and biological effects of a second bacteriocin from Enterococcus faecalis ssp. liquefaciens S-48 and its mutant strain B-48-28.

Enterococcus faecalis ssp. liquefaciens S-48 (producer of the peptide antibiotic AS-48) and its mutant B-48-28 (AS-48-) secrete the bacteriocin Bc-48. This substance has been purified to homogeneity from culture supernatants of strain B-48-28; it consists of a protein (80 kDa) stable from pH. 5.5 to 9.0 and sensitive to temperatures above 45 degrees C and to proteases. Its inhibitory spectrum is restricted to strains of Enterococcus faecalis. Bc-48 inhibits protein synthesis but does not affect amino acid uptake. A partial reduction of cell viability, together with autolysis, is also observed. Bc-48 differs from peptide AS-48 in both its molecular properties and mode of action.     

Comparison of perturbation effect of propranolol, verapamil, chlorpromazine and carbisocaine on lecithin liposomes and brain total lipid liposomes. An EPR spectroscopy study.

Effect of verapamil, propranolol, chlorpromazine and carbisocaine on dynamics and/or order of liposomes (perturbation effect), prepared from different molar ratios of lecithin (PC) and rat brain total lipids (TL) was studied by EPR spectroscopy using spin probes 16-doxyl stearic acid and 14-doxyl phosphatidylcholine. The PC liposomes had higher dynamics and/or lower order than the TL liposomes. The perturbation effect of the drugs depended largely on the lipid composition of the liposomes. The drugs at the drug/lipid molar ratios from 0.1 to 1 increased membrane dynamics and/or decreased membrane order. The drugs had the most pronounced perturbation effect in the liposomes prepared from brain total lipids. The effect of the drugs decreased with decreasing the TL/PC ratio in the liposomes and was lowest, almost diminished, in the PC liposomes. Increasing concentration of the drugs decreased the difference between the dynamics and/or order of the PC and TL liposomes and so eliminated the influence of lipid composition on these membrane parameters. The results emphasize the role of lipid composition in studies concerning drug-lipid interactions in model and biological membranes.     

Trypsin-SBTI interaction in reverse micelles. A slow intermicellar exchange-dependent binding

Solubilisate exchange between reverse micelles must take place before any reaction inside reverse micelles occurs if the reactants are confined to the aqueous micellar core. When the interacting species are 2 small molecules or one small molecule and one macromolecule, it has been shown that the exchange is faster than the typical turnover of an enzymatic reaction. The study of the interaction between 2 macromolecules (trypsin and soybean trypsin inhibitor) in reverse micelles carried out in this work reveals that the exchange between these macromolecule-containing reverse micelles slows down by a thousand times and the limiting-step in the exchange, the fusion, by 10(6) times. Both reverse micellar size (omega 0 = [water]/[surfactant]) and temperature affected the rate of the fusion process. A hypothesis for the proposed active role of macromolecules in the exchange process is also given.     

Structure-function analysis of the human integrin VLA-4 (alpha 4/beta 1). Correlation of proteolytic alpha 4 peptides with alpha 4 epitopes and sites of ligand interaction.

The structure-function relationship of the human integrin VLA-4 (alpha 4/beta 1; CD49d/CD29), has been studied in the human B-cell line Ramos by immunochemical and functional analysis. Ramos cells expressed the 150-kDa non-proteolyzed form of the alpha 4 chain, which could be digested upon mild trypsin treatment to generate the 80- and 65-kDa proteolyzed forms, as well as alpha 4 polypeptides of 55 and 50 kDa. In addition, treatment of Ramos cells with high doses of pronase predominantly yielded the 55- and 50-kDa alpha 4 peptides. The trypsin-generated 80- and 65-kDa alpha 4 polypeptides, but not the 55- and 50-kDa fragments, were able to associate with the beta 1 chain. Distinct anti-VLA-4 mAb against four different alpha 4 epitopes, referred to as epitopes A, B1, B2, and C, recognized the 150-kDa alpha 4 chain both associated or non-associated with the beta 1 chain. The alpha 4 proteolytic forms of 80, 65 and 50 kDa were precipitated by the anti-alpha 4 mAb directed against the four different alpha 4 epitopes. On the other hand, the 55-kDa alpha 4 peptide was present in precipitates from anti-alpha 4 mAb specific for epitopes A, B1 and C, but absent in precipitates from the anti-alpha 4 mAb specific for epitope B2. The different adhesive capacities of the VLA-4 integrin, namely the interaction with a 38-kDa fibronectin fragment containing the CS-1 region of plasma fibronectin (Fn-38), the binding to the vascular cell adhesion molecule-1 (VCAM-1), or the ability to mediate the anti-alpha 4-induced cell aggregation, were not altered on VLA-4 from cells upon mild trypsin treatment, when compared to non-treated cells. However, the 55- and 50-kDa alpha 4 forms generated by high-dose pronase cell treatment, failed to mediate cell interaction with Fn-38 or VCAM-1 ligands, and cell aggregation could not be triggered through VLA-4 under these conditions.     

Characterization of catalase-negative mutants of methylotrophic yeastHansenula polymorpha

Three recently isolated catalase-negative mutants ofHansenula polymorpha lost the ability to grow on methanol but grew in media containing glucose, ethanol or glycerol. Their incubation in a medium with methanol resulted in an accumulation of hydrogen peroxide and cell death. During growth of a catalase-negative mutant in chemostat on a mixture of methanol and glucose, neither H₂O₂ accumulation nor cell death were observed up to the molar ratio of 10:1 of the two substrates. Cytochrome-c peroxidase and NADH-peroxidase activities were detected in the cells. In methylotrophic yeasts, catalase seems to be an enzyme characteristic of the metabolism of methanol but not needed for the metabolism of multicarbon substrates. The hydrogen peroxide produced during growth of the mutants on mixed substrates is detoxified by cytochrome-c peroxidase and other peroxidases. Translated by Č. Novotny     

Deoxyribonuclease activities in Myxococcus coralloides D

Myxococcus coralloides D produced cell-bound deoxyribonucleases (DNases) during the exponential phase of growth in liquid medium. DNase activity was much higher than that detected in other myxobacterial strains and was fractionated into three different peaks by filtration through Sephadex G-200. The DNases were named G, M and P. The optimum temperatures were 37 degrees C, 33 degrees C and 25 degrees C respectively, although high activities were recorded over the temperature range 20-45 degrees C. The pH range of high activity was between 6.0 and 9.0, with an optimum for each DNase at 8.0. DNases M and P were strongly inhibited by low concentrations of NaCl, but activity of DNase G was less affected by NaCl. The three activities required divalent metal ions as cofactors (especially Mg2+ and Mn2+); however, other metal ions (Fe2+, Ni2+, Zn2+) were inhibitors. The molecular weights were estimated by gel filtration chromatography and SDS-PAGE as 44 kDa (DNase G), 49 kDa (DNase M) and 39 kDa (DNase P).     

ms2i6A deficiency enhances proofreading in translation.

The hypermodified base 2-methylthio-N6-isopentenyladenosine (ms2i6A) at position 37 occurs frequently in tRNAs that read codons starting with uridine. Here we have studied how ms2i6A affects the accuracy of poly(U) translation in vitro. Deficiency leads to a higher rejection rate of tRNA4(Leu) by more aggressive proofreading on the wild-type ribosome, but with the initial selection step unchanged. Our data indicate that ms2i6A has no effect on codon-anticodon interactions on wild-type ribosomes as long as aminoacyl-tRNA is in ternary complex with EF-Tu and GTP. ms2i6A deficiency in the cognate poly(U) reader tRNA(Phe) leads to increased misreading when the near-cognate competitor tRNA4(Leu) is wild-type. ms2i6A deficiency in tRNA4(Leu) gives a decreased error level in competition with wild-type tRNA(Phe).