Some characteristics of monolayers of 1-palmitoyl-2-oleoyl-phosphatidylglycerol with and without dipalmitoylphosphatidylcholine during dynamic compression and expansion

Some properties of monolayers of $\text{1-}\text{palmitoyl}\text{-2-}\text{oleoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phospho}\text{-rac-}\text{glycerol}$ (POPG) alone or of POPG in mixtures with $\text{1,2-}\text{dipalmitoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phosphocholine}$ (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm²·s^?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m^?1 in the presence of Na⁺, Ca²⁺ or low pH (2.0) in the subphase. (3) The presence of Ca²⁺ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na⁺ or Ca²⁺ in the subphase.     

A New Species of Kudoa (Myxosporidea: Chloromyxidae) from the Spot,Leiostomus xanthurus Lacépède,in Clear Lake,Texas*

SYNOPSIS. Kudoa branchiata sp. n. (Myxosporidea: Chloromyxidae) is described from the gills of the marine sciaenid fish, Leiostomus xanthurus Lacépède, from Clear Lake, Texas. Twelve of the 429 hosts examined from 10 September 1970 to 28 April 1971, were infected. Eight of the 12 infected fish were collected in February and March 1971—a period during which only 13% of the total host sample was taken. The mean total length of infected hosts was 149 mm, with a range of 112–185 mm. The mean number of myxosporidean cysts per infected host was 3.5, with a range of 1–11.     

Occurrence of an inhibitor of lactic Acid bacteria in green olives

Green olives were found to contain an inhibitor(s) of several species of lactic acid bacteria usually associated with the Spanish-type brined olive fermentation. The inhibitor was demonstrated by the presence of inhibition zones surrounding tissue which had been cut from frozen olives and implanted in a seeded nutritive agar medium. Relative potencies of aqueous extracts of frozen olives were determined by a paper disc assay method. The Mission variety of olive contained the most inhibitor, and the Manzanillo and Ascolano, about 50 and 40% as much as the Mission variety, respectively. Sevillano and Barouni varieties contained comparatively little inhibitor. Effects of the inhibitor on growth rates of lactic acid bacteria were determined by adding various amounts of a concentrated aqueous extract of olives to a nutritive broth medium contained in screw-capped tubes. Of the four species of lactic acid bacteria tested, Leuconostoc mesenteroides was the most sensitive, and Lactobacillus plantarum was the least sensitive; Pediococcus cerevisiae and Lactobacillus brevis were intermediate in sensitivity. Extracts possessed a bactericidal property, as evidenced by their effect on L. mesenteroides. Sodium chloride, especially at concentrations of about 5% and higher, greatly increased the effectiveness of the inhibitor. The inhibitor was ethyl alcohol-soluble and was stable when heated at 100 C in aqueous solution. Potencies of extracts were reduced greatly by adjustment to pH 10, but no appreciable effect was noted by adjustment to pH 0.8.     

Electro-optical studies of conformation and interaction of polynucleotides

Measurements by the technique of electric birefringence with pulsed sinusoidal electric fields on polyriboadenylic acid (poly-A) and polyribouridylic acid (poly-U) indicate that the kinetics of the double-stranded helix formation of poly (A + U) in the presence of Mg²⁺ is second order and consists of two steps: nucleation and propagation of base pairs from nuclei. The nucleation involves approximately 7 base pairs. It seems that the requirement of 7 base pairs to start the formation of a double-stranded helix is not peculiar to poly (A + U) but is associated with double-stranded helices of polynucleotides in general. This implies that it may be associated with spatial requirements of the phosphate-sugar backbone, rather than with the particular bases linked to the backbone. The decline in rate of poly (A + U) formation observed above a critical temperature is the consequence of changes in the poly-A conformation setting in at this critical temperature, rather than resulting from an increase in the reversibility of the base-pair propagation step of double-stranded helix formation. The dominant role of the conformation of poly-A in the double-stranded helix formation of poly (A + U) is further borne out by the pH dependence of the rate which completely parallels the conformation changes known to occur in poly-A as a function of pH. This indirectly suggests that at neutral pH poly-A is a single-stranded helix. The rotary diffusion coefficients attest to the flexibility of this helix, while the stacked nature of the base pairs at low temperatures is revealed by the identical increments in the specific Kerr constant on going from poly-A to poly (A + U) and from poly (A + U) to poly (A + 2U) helices. Results suggest that Mg²⁺ binds to the phosphate part of the backbone. Poly-U binds Mg²⁺ more strongly than poly-A; this difference in binding strength is attributed to differences in conformation (random coil versus helix). It is also borne out by the present results that the degree of order in the structure of poly-U, even at low temperatures and neutral pH, is at best an order of magnitude smaller than that of poly-A under similar conditions. Furthermore, the earlier proposed double-stranded structure of poly-U is called into question. A hairpinlike structure seems to agree with results of this investigation. Finally, the results support the contention that the ion atmosphere polarization is responsible for orientation of polyelectrolytes in the presence of alternating electric fields in the neighborhood of 25 kc./sec. frequency.     

Down-regulation of IL-2 production by activation of T cells through Ly-6A/E

Ly-6A/E molecules are expressed on the surface of T cells and have been shown to function in activation by the capacity of anti-Ly-6A/E mAb to induce T cell hybridomas or normal T cells to produce IL-2. Recent evidence suggests that activation through Ly-6A/E may be linked to the TCR signaling pathway. To further investigate the relationship between Ly-6- and TCR-induced T cell activation, we have examined whether an anti-Ly-6A/E mAb (D7) modulates TCR signaling in vitro. We now report that mAb D7 specifically inhibited IL-2 production by T cells also activated through TCR. Such inhibition was noted for normal T cells stimulated by soluble anti-CD3 or alloantigen and for T hybridomas stimulated by soluble anti-CD3. The ability of D7 to inhibit IL-2 production by T hybridomas was dependent on the nature of the TCR activating signal because IL-2 production was not inhibited when T hybridomas were stimulated with Ag or immobilized anti-CD3. Inhibition of IL-2 production by D7 apparently required cross-linking of the mAb because D7 F(ab')2 fragments were not effective for inhibition of IL-2 production. Similar to its ability to enhance anti-Ly-6A/E-induced activation of T and B cells, IFN-gamma enhanced the D7-induced inhibition of IL-2 production by alloantigen-activated normal T cells. These data further support the notion that Ly-6 and TCR signaling pathways are interrelated.     

G regulatory proteins and muscarinic receptor signal transduction in mucous acini of rat submandibular gland

The involvement of G regulatory proteins in muscarinic receptor signal transduction was examined in electrically permeabilized rat submandibular acinar cells. The guanine nucleotide analog, GTP gamma S, caused the dose dependent hydrolysis of membrane phosphatidylinositol 4,5-bisphosphate to release IP3. This response was insensitive to pertussis toxin treatment and was duplicated by NaF but not by GDP beta S. Enhanced IP3 synthesis was observed with a combination of GTP gamma S and carbachol. Exogenous IP3, as well as carbachol and GTP gamma S, provoked the release of sequestered 45Ca2+ from non-mitochondrial stores. In intact cells, carbachol significantly reduced the level of cyclic AMP induced by the beta-adrenergic agonist, isoproterenol, to 69% of its normal value. Pertussis toxin abolished this inhibitory action of carbachol on cyclic nucleotide levels. These results suggest that muscarinic receptors are coupled to two separate G regulatory proteins in submandibular mucous acini-the pertussis toxin-insensitive Gp of the phosphoinositide transduction pathway associated with elevated cytosolic calcium levels, and the pertussis toxin-sensitive Gi inhibitory protein of the adenylate cyclase complex.     

Fluorescence studies of rat cellular retinol binding protein II produced in Escherichia coli: an analysis of four tryptophan substitution mutants.

Rat intestinal cellular retinol binding protein II (CRBP II) is an abundant 134-residue protein that binds all-trans-retinol which contains 4 tryptophans in positions 9, 89, 107, and 110. Our ability to express CRBP II in Escherichia coli and to construct individual tryptophan substitution mutants by site-directed mutagenesis has provided a useful model system for studying the fluorescence of a multi-tryptophan protein. Each of the four mutant proteins binds all-trans-retinol with high affinity, although their affinities are less than that of the wild-type protein. Steady-state and time-resolved fluorescence analyses of these proteins indicate that W107 is at the hydrophobic binding site, W110 is in a polar environment, and the remaining two tryptophans are in a hydrophobic environment. Time-resolved fluorescence study indicates that excited-state energy transfer occurs from the hydrophobic tryptophans to W110. The Stern-Volmer analysis with acrylamide of these proteins reveals that static quenching occurs in the W9F mutant protein while others do not. The fluorescence of rat intestinal fatty acid binding protein (I-FABP), a related protein of known X-ray structure, was also studied for comparison. The results of these findings, coupled with those derived from NMR studies and molecular graphics, suggest that CRBP II undergoes minor structural changes in all of the mutant proteins. Since these effects may be cumulative on the protein structure and function, any conclusions derived from higher mutants in this family of proteins must be treated with caution.     

Uneven distribution of protein kinase C-α and -β isozymes in human sarcomas and carcinomas

Protein kinase C (PKC) represents a family of structurally related Ser/Tre kinases which are involved in mitogenic signalling and may contribute to human neoplasia. To address this issue, the messenger RNA and protein levels of PKC isoenzymes α and β were analyzed in several human sarcoma- and carcinoma-derived cell lines. Carcinomas contained low or undetectable levels of either PKC-α or PKC-β. Sarcomas exhibited similar or increased PKC expression compared to human diploid fibroblasts. Moreover, sarcoma cell lines expressing one PKC isoform did not contain detectable levels of the other. When PKC was depleted from the tumor cells, we observed that the PKC overexpressing sarcomas had reduced their malignant properties as determined by their ability to grow in semisolid medium. In addition, epidermal growth factor-stimulated and erbB2-transformed fibroblasts exhibited enhanced cell growth in the absence of PKC. We propose a model for the effect of PKC as a negative regulator of proliferation in epithelial cells and a growth promoter in fibroblasts. © 1994 wiley-Liss, Inc.