Electrical stability of erythrocytes in the presence of divalent cations

Erythrocytes suspended in a medium of low ionic strength lyse under the effect of an exponential electrical pulse. The percentage of haemolysed cells decreases several-fold in the presence of divalent cations. The protective action of the ions studied increases in the following order: Ca⁺⁺, Mg⁺⁺, Zn⁺⁺. It is assumed that divalent ions bind to the negative charges of the lipid and protein molecules and reduce their electrostatic repulsion, which results in stabilization of the membranes.     

Hybrid vectors for the cyanobacterium Anacystis nidulans R2, containing the plasmid pUB110 from Staphylococcus aureus

The recombinant vector plasmids were constructed having the DNA of pUB110 plasmid (4,5 kb, KmR) from Staphylococcus aureus inserted into the cryptic plasmids pANS (8 Kb) and pANL (48,5 kb) of cyanobacterium Anacystis nidulans R2. The hybrid plasmids transform cyanobacterial cells to Km-resistance with high efficiency. The plasmid pBS20, containing the complete sequence of pANS and pUB110 DNA, transforms Bacillus subtilis rec E4 protoplasts being, however, unstable in bacilli cells and disintegrates deriving a parent pUB110 plasmid.     

A modified method of isolation of "tight" 70S ribosomes from Escherichia coli highly active at different stages of the elongation cycle

The functional activity of the wide-spread "tight" 70S ribosomes is usually equal to 55-80%. We show here that the inactive fraction of this type of ribosomes is virtually blocked by residual endogenous RNA's. These RNA's are shown to be removable by introducing an additional stage in the isolation procedure including: 1. short heating (15 min, 37 degrees C) of "tight" 70S under dissociation conditions, i. e. in a buffer containing 3 mM MgCl2 and 200 mM NH4Cl; 2. washing off endogenous RNA's on a sucrose density gradient in the same buffer; 3. final selection of purified "tight" 70S on the sucrose gradient containing 5 mM MgCl2 and 50 mM NH4Cl. "Tight" 70S ribosomes isolated by such a procedure are 90-100% active with respect to tRNA binding (including the factor-dependent one), peptide bond synthesis and translocation.     

Antibodies to pollen exines

A polyclonal antiserum and monoclonal antibodies have been prepared to purified pollen exines of Calocedrus decurrens Florin. The location of the antigen is in the exine, as shown by light-and electron-microscopic immunocytochemistry. The greatest reduction in antibody binding follows treatment of the exine with chemicals known to alter sporopollenin. These results provide evidence that sporopollenin is antigenic. Exines of ten species of gymnosperms and angiosperms also bound the polyclonal antiserum, indicating similarity of sporopollenin structure.     

Drosophila basement membrane procollagen IV. I. Protein characterization and distribution

A collagen was isolated from Drosophila E85, Schneider line 2L and Kc cell cultures. The purified protein was characterized and antibodies were raised against it. Immunofluorescence microscopy locates this material to the regions of basement membranes of Drosophila embryos, larvae, and adults. The molecules are mostly, or entirely, homotrimers of one polypeptide chain linked by interchain disulfide bonds. The partial amino acid sequences of a cyanogen bromide cleavage product of this chain are identical with a part of the virtual translation product of the Drosophila pro alpha 1(IV) nucleotide sequence that is reported in the accompanying paper. This gene is at Drosophila chromosome location 25C and was identified by the high homology of one part of it with the noncollagenous carboxyl terminus (NC1) of vertebrate type IV basement membrane collagens (Blumberg, B., MacKrell, A. J., Olson, P. F., Kurkinen, M., Monson, J. M., Natzle, J. E., and Fessler, J. H. (1987) J. Biol. Chem. 262, 5947-5950). In the electron microscope each molecule appears as a thread with a knob at one end, which contains the carboxyl peptide domains. The variation of flexibility of the thread was mapped along its length. Pulse-chase labeling of cell cultures showed that these molecules associate into disulfide-linked dimers and higher oligomers that can be partly separated by velocity sedimentation and are resolved by sodium dodecyl sulfate-agarose gel electrophoresis. Dimers and higher oligomers formed by overlap of the amino ends of molecules were found. Mild pepsin digestion of Drosophila embryos and larvae solubilized the corresponding disulfide-linked collagen molecules, and Staphylococcus aureus V8 protease peptide maps showed the identity of the collagen derived from animals and from cell cultures. Individual, native molecules have a sedimentation coefficient s20,w = 4.1 S, the dichroic spectrum and amino acid composition of a collagen, and a Tm = 31 degrees C. Positive in situ hybridization with a specific probe for this collagen began 6-8 h after egg laying and showed message in the locations of embryos and larvae which reacted with the antibodies. This included some prominent individual cells in the hemolymph.     

Expression of C gamma 4 T cell receptors and lack of isotype exclusion by dendritic epidermal T cell lines

Although four murine C gamma gene segments (C gamma 1, 2, 3, and 4) are known to exist, the large majority of expressed gamma-chains have been shown to be of the C gamma 1 isotype and no evidence exists for the expression of more than one receptor by gamma delta TCR-bearing cells. We investigated the nature of the TCR expressed on a number of murine dendritic epidermal T cell-derived cell lines by using both Northern blot and immunoprecipitation analyses. One of these CD3+ cell lines (T195) expresses C gamma 4, V gamma 1, and delta mRNA, and its CD3-associated TCR complex can be precipitated by both anti-C gamma 4 and anti-delta sera, indicating that this receptor is a C gamma 4/delta heterodimer. Furthermore, we show that two cell lines (Y245, Y93) express two distinct TCR gamma-chains, one derived from the C gamma 4 locus, whereas the second gamma-chain is probably derived from the C gamma 2 locus. Together with the previous demonstration of C gamma 1/delta TCR on a number of dendritic epidermal T cell lines (DETC), these results indicate that such DETC are capable of expressing a variety of gamma delta TCR and that, in some DETC, isotype exclusion of gamma-chain expression does not occur.     

Pre-lysosomal divergence of alpha 2-macroglobulin and transferrin: a kinetic study using a monoclonal antibody against a lysosomal membrane glycoprotein (LAMP-1)

We have used electron microscopic immunocytochemistry to compare the distribution of LAMP-1, a marker for lysosomal membranes, with the intracellular localization of alpha 2-macroglobulin (alpha 2-M) and transferrin at various time points after their endocytosis into cultured NIH 3T3 cells. The purposes of this study were (a) to determine how soon endocytic ligands reach lysosomal organelles, (b) to examine whether the intermediate endocytic vesicles gained lysosomal markers gradually or in a precipitous, discrete event, and (c) to examine the relationship, if any, between the pathway of recycling ligands and lysosomes. At early time points (0-5 min) after initiation of endocytosis, most structures containing alpha 2-M labeled with colloidal gold (receptosomes) were not labeled by anti-LAMP-1 detected using ferritin bridge or peroxidase immunocytochemistry. At late time points (greater than or equal to 15 min), the structures containing alpha 2-M (lysosomes) were strongly labeled by anti-LAMP-1. In contrast, transferrin that was directly labeled with ferritin was mostly located in LAMP-1-negative structures at all time points studied. The proportion of alpha 2-M-gold containing vesicles strongly labeled for LAMP-1 roughly paralleled the proportion of alpha 2-M-gold-containing structures positive for cytochemically detectable acid phosphatase. Our data indicate that ligands such as transferrin that are internalized through coated pits and receptosomes, but not delivered to lysosomes, do not traverse a lysosomal organelle compartment as marked by LAMP-1 content. Ligands such as alpha 2-M that are destined for lysosomal delivery reach a LAMP-1-positive organelle compartment only after they traverse LAMP-1-negative, non-lysosomal vesicles previously described as receptosomes.     

Studies on the link between HMG-CoA reductase and cholesterol 7 alpha-hydroxylase in rat liver

Under most experimental conditions, there is a covariation between the rate-limiting enzyme in cholesterol biosynthesis, HMG-CoA reductase, and the rate-limiting enzyme in bile acid biosynthesis, cholesterol 7 alpha-hydroxylase. The most simple explanation for the coupling between the two enzymes is that newly synthesized cholesterol is a substrate for an unsaturated cholesterol 7 alpha-hydroxylase and that substrate availability is of major regulatory importance for this enzyme. The following results seem, however, to rule out that such a simple regulatory mechanism is of major importance and that HMG-CoA reductase activity per se is of importance in the regulation of cholesterol 7 alpha-hydroxylase. 1) The apparent degree of saturation of cholesterol 7 alpha-hydroxylase, as measured in vitro in rat liver microsomes, was found to be relatively high (70-90%) under most experimental conditions, including starvation, cholestyramine treatment, and cholesterol treatment. A significant decrease in the degree of saturation was obtained first after a drastic reduction of total concentration of cholesterol in the microsomes by treatment with high doses of triparanol, an inhibitor of cholesterol biosynthesis. 2) The stimulatory effect of cholesterol feeding on cholesterol 7 alpha-hydroxylase activity in rats seems to be an effect on the enzyme activity (enzyme induction?) rather than an effect on substrate availability. Thus, the stimulatory effect of cholesterol feeding was retained also after almost complete removal of the endogenous cholesterol by extraction with acetone.(ABSTRACT TRUNCATED AT 250 WORDS)