Effect of polymyxin B on the structure and the stability of lipid layers

Summary Polymyxin B (PX) does not penetrate phospholipid monolayers and bilayers at low field strength across the lipid layers. The degree of penetration of PX is evaluated from its effect on the capacitance of the monolayers and on the conductance of the bilayers. PX added to one side of a bilayer causes its destabilization, it also enhances destabilization of lipid monolayers at positive electric fields across the surface layer in the direction of the adsorbed PX. PX lowers very little the fluorescence polarization of 1,6-diphenyl 1,3,5 hexatriene embedded in phospholipid vesicles. It is suggested that the penetration mechanism of PX into gram-negative bacteria is based on transient local breakdown of the plasma membrane.     

Adult thymectomy promotes the manifestation of autoreactive lymphocytes.

Spleen cells from adult thymectomized mice (ATX) were assayed in a syngeneic graft vs host (GVH) model based upon enlargement of the draining popliteal lymph node following syngeneic cell inoculation into the hind footpad. Spleen cells from ATX mice have been found to induce a significantly higher increase in the weight of the regional lymph node than that induced by the injection of normal spleen cells. Irradiated spleen cells from ATX donors did not cause a similar increase, suggesting either that proliferation of the transferred cells was required at some stage of the reaction or that autoreactive cells are radiosensitive. Autoreactive cells were found in the spleen of mice 2 to 3 months after the thymectomy but were never found in the lymph nodes of such animals or in the thymus of intact mice. They are not phagocytic adherent cells and are not retained on nylon wool columns, which suggests that they belong to the T-cell lineage. Autoreactivity is lost when spleen cells from ATX donors are depleted of autologous rosette-forming cells (A-RFC) by centrifugation on a Ficoll-Hypaque gradient after rosette formation. Autoreactive spleen lymphocytes might belong to the population of A-RFC previously characterized as a population of immature T cells.     

CD3 negative "small agranular lymphocytes" are natural killer cells

We describe here that CD3-, CD16+ and/or CD56+ small lymphocytes, in a highly reproducible fashion, mediate a significant level of K562 killing that is, on a "per cell" basis, comparable to the cytolytic activity of CD3- LGL. The CD3- small lymphocytes appeared to have no granules based on light and electron microscopy and lack of right-angle scatter on the FACS; we thus refer to them as small "agranular" lymphocytes (SAL). The lytic activity against K562 is inhibited by treatment with either L-leucine methyl ester or EGTA, which are reported to effect granule-dependent killing. We suggest that the SAL have lytic molecules in their cytoplasm (which are sensitive to these treatments) but that these molecules are not organized into discrete granules as found in LGL. The CD3- SAL are phenotypically very similar to LGL and both SAL and LGL mediated equal and reproducible antibody-dependent cell-mediated cytotoxicity. These observations force redefinition of the concept of NK cells to include both CD3- LGL and CD3- SAL.     

Metabolic heterogeneity of isolated cortical and juxtamedullary glomeruli in adriamycin nephrotoxicity.

The anticancer drug adriamycin (ADR) is selectively toxic to glomerular cells when administered intravenously (5 mg/kg b.w.) to female MWF/Ztm rats. Recent data have shown that the proteinuria associated with the lesion does not occur in cortical glomeruli, suggesting the selective injury of juxtamedullary glomeruli. In the present study, the effect of ADR on glomerular metabolism was studied with special reference to possible differences between cortical and juxtamedullary glomeruli. On day 7 after ADR treatment, cortical and juxtamedullary glomeruli were separately isolated by the sieving method and 14C glucose oxidation to 14CO2 and the incorporation of 3H proline into macromolecules were measured in vitro and used to study target selective injury in ADR-treated rats compared to control rats. The investigations revealed differences in the response of cortical and juxtamedullary glomeruli to ADR. ADR treatment increased proline incorporation over a 4-hour incubation period in both glomerular populations compared to controls, but the effect was significantly (p less than 0.05) more pronounced in juxtamedullary glomeruli (juxtamedullary: 187 +/- 8% of control; cortical: 167 +/- 4% of control). Glucose oxidation was enhanced after 4 h only in juxtamedullary glomeruli (juxtamedullary: 132 +/- 3% of control; cortical: 82 +/- 10% of control). These data show that glomerular damage caused by ADR is associated with a stimulating effect on glomerular metabolism which is more marked in juxtamedullary than in cortical glomeruli, thus indicating a heterogenous response of different glomerular populations and supporting the concept that the selective damage of juxtamedullary glomeruli accounts for the proteinuria.     

Pulmonary angiotensin-converting enzyme substrate hydrolysis during exercise.

We examined exercise-induced changes in indicator-dilution estimates of the angiotensin-converting enzyme first-order kinetic parameter, the ratio of a normalized maximal enzymatic conversion rate to the Michaelis constant (Amax/Km), which, under stable enzymatic conditions, will vary with the pulmonary vascular surface area accessible to vascular substrate, the extravascular lung water (an index of the proportion of lung tissue perfused), and the central blood volume (from pulmonary trunk to aorta). Experiments were performed in 10 mongrel dogs at rest and through two increasing levels of treadmill exercise, with the use of two vascular space tracers (labeled erythrocytes and albumin), a water space tracer ([1,8-14C]-octanediol), and a vascular endothelium surface area marker, benzoyl-Phe-Gly-Pro ([3H]BPGP), which is a pharmacologically inactive angiotensin-converting enzyme substrate. The exercise-induced increase in cardiac output was accompanied by a linear increase in central blood volume, and dilutional extravascular lung water rapidly increased to an asymptotic proportion close to 100% of postmortem vascular lung water. There was an average 55% [3H]BPGP hydrolysis, which did not vary with flow, and the computed Amax/Km increased linearly with exercise. We conclude that exercise results in complete lung tissue recruitment and increases the pulmonary vascular surface area available for BPGP hydrolysis linearly with flow, so that pulmonary vascular recruitment continues after full tissue recruitment.     

The hypolimnetic protozoan plankton of a eutrophic lake

The seasonal distribution of benthic species in the water column above and below the thermocline in a small eutrophic lake is described. During summer stratification populations of Spirostomum spp, Loxodes spp., Plagiopyla and Deltopylum become established in the plankton on or below the oxycline/thermocline. At shallow sites no migration occurred and populations of the migratory species in the benthos were sparse, with the exception of Plagiopyla which occurred in high densities in the sediment. Two distinct planktonic populations are established during stratification: an epilimnetic community of obligate planktonic ciliates and a hypolimnetic community of benthic migrants.     

MAXAMIZE. A DNA sequencing strategy advisor.

The MAXAMIZE advisory system determines from user-provided restriction maps an optimal strategy to do nucleotide sequencing by methods involving end-labeled fragments. The maps may be either simple linear restriction maps of fragments or complex circular maps including restriction sites of a vector. The whole system is interactive and is written in the Genetic English language provided by the GENESIS System, a molecular genetics knowledge representation and manipulation package. In addition, MAXAMIZE provides bookkeeping facilities for sequencing and offers advise on how to verify the newly obtained sequence data.     

Nickel,cobalt, and molybdenum requirement for growth of Methanobacterium thermoautotrophicum

Growth of Methanobacterium thermoautotrophicum on H₂ and CO₂ as sole energy and carbon sources was found to be dependent on Ni, Co, and Mo. At low concentrations of Ni (<100 nM), Co (<10 nM) and Mo (<10 nM) the amount of cells formed was roughly proportional to the amount of transition metal added to the medium; for the formation of 1 g cells (dry weight) approximately 150 nmol NiCl₂, 20 nmol CoCl₂ and 20 nmol Na₂MoO₄ were required. A dependence of growth on Cu, Mn, Zn, Ca, Al, and B could not be demonstrated. Conditions are described under which the bacterium grew exponentially with a doubling time of 1.8 h up to a cell density of 2 g cells (dry weight)/1.     

Human placental N-acetyl-beta-D-hexosaminidase isozymes. Activity toward native hyaluronic acid.

The activity of purified human hexosaminidases A and B toward hyaluronic acid (HA) isolated from cultured human skin fibroblasts was investigated. The cleavage of N-acetylglucosaminyl residues to monosaccharide N-acetylglucosamines by hexosaminidase isozymes was determined in the presence and absence of purified human β-glucuronidase. The pH optima of this reaction, with and without β-glucuronidase, were 4.5 for hexosaminidase A and 4.0 for hexosaminidase B. The hydrolysis of HA by both hexosaminidase isozymes proceeds linearily for at least 18 h in the presence of β-glucuronidase. Concentrations of 0.5–5 units of either isozyme showed a linear relationship with rate of hydrolysis. Without β-glucuronidase, hexosaminidase only cleaved the terminal N-acetylglucosamine residue. However, under optimal conditions, with β-glucuronidase, the hydrolytic activity of hexosaminidase B was about 30% as efficient as that of hexosaminidase A. Approximately 70% of the HA could be degraded by 5 units of hexosaminidase A in the presence of 0.5 unit of β-glucuronidase, as opposed to 25% degraded by hexosaminidase B. These results probably reflect intrinsic differences in the activities of the two isozymes. Since the substrate (HA) did not inhibit the hydrolysis of a synthetic substrate (4-methylumbelliferyl-β-glucosaminide) by hexosaminidase B, the linear kinetics of HA hydrolysis implies no product inhibition. These data indicate that native HA can be hydrolyzed by the combined activities of β-glucuronidase with hexosaminidase A or hexoaminidase B.     

Differential scanning calorimetry of dipalmitoyl phosphatidylcholine analogues and of their interaction products with basic polypeptides

The thermotropic behaviour of dipalmitoyl phosphatidylcholine analogues with a varying number (n) of CH₂ groups between the phosphate and the quaternary ammonium has been investigated. The temperature (T_m) and the enthalphy (ΔH) of the phase transition are non-monotonous functions of the number of CH₂ groups. T_m oscillates between 40 and 45°C and ΔH between 7 and 13 kcal/mol for a variation of n between 2 and 11.It is concluded that the hydrocarbon chains in the head groups do not penetrate the hydrocarbon region and do not contribute directly to the melting of the acyl chains. It is suggested that their length may affect the critical ballance between the attractive and the repulsive forces within the bidimensional lattice of the head groups.Copolypeptides of lysine with phenylalanine do not appreciably affect the T_m but have a pronounced effect on ΔH of the lipid phase transition, which depends strongly on the ratio of the two amino acids in the polypeptide. The effect of copolypeptide of any defined composition on ΔH is also a non-monotonous function of the number of CH₂ groups in the phosphatidylcholine head group, but it does not parallel completely the oscilations in the T_m and ΔH of the pure lipids.