Reproduction and spacing behaviour of females in a peak density population of Clethrionomys glareolus

A peak density population of Clethrionomys glareolus was studied by snap-trapping to determine by experimentation whether spacing behaviour regulated the breeding density. On control plots onset of reproduction was asynchronous, litter size of overwintered females decreased significantly during the summer and no year-born animals matured during the reproductive period. A removal experiment in the early summer resulted in sexual maturation of year-born females. A second removal in late summer indicated an inhibition of maturation in year-born females despite continued intense reproduction of overwintered females. We conclude that spacing behaviour regulated maturation of females early in the summer but other factors, such as food quality, limited maturation in late summer.     

Formation of (4R)- and (4S)-4-hydroxyochratoxin A and 10-hydroxyochratoxin A from Ochratoxin A by rabbit liver microsomes.

Three metabolites were formed from ochratoxin A in the presence of rabbit liver microsomal fractions and NADPH. They were isolated by extraction, thin-layer chromatography, and high-pressure liquid chromatography. Two of them were identified as (4R)- and (4S)-4-hydroxyochratoxin A. It is suggested on the basis of mass and nuclear magnetic resonance spectroscopy that the third metabolite is 10-hydroxyochratoxin A. The formation of the metabolites was inhibited by carbon monoxide and metyrapone and was stimulated when microsomes from phenobarbital-treated animals were used. The results suggest that cytochrome P-450 catalyzes the formation of these metabolites.     

Some Properties of Thiosulfate-Oxidizing Enzyme from Marine Heterotroph 16B

Thiosulfate-oxidizing enzyme has been demonstrated in cell-free extracts of the marine, thiosulfate-oxidizing pseudomonad strain 16B. The enzyme, partially purified by ion-exchange chromatography and calcium phosphate gel treatment, catalyzed the oxidation of thiosulfate to tetrathionate with the concomitant reduction of ferricyanide. Native but not mammalian cytochrome c was also reduced by the enzyme in the presence of thiosulfate. The enzyme was located exclusively in the supernatant of ultracentrifuged cell extracts. The most purified enzyme preparation, like intact cells, exhibited a temperature optimum of 30 to 31°C. However, it exhibited no definite pH optimum. At pH 6.1 to 6.3 and 30°C, the K_m for thiosulfate was 1.57 mM. At lower temperatures, the apparent K_m for thiosulfate increased, but the apparent maximum velocity remained virtually unchanged. Thiosulfate oxidation in intact cells exhibited an increase in the pH optimum at lower temperatures. The thiosulfate-oxidizing enzyme of marine heterotroph 16B is compared with thiosulfate-oxidizing enzymes from other bacteria, and the effect of temperature on the relationship between pH and thiosulfate oxidation is discussed with reference to the natural habitat of the bacterium.     

Abortive Infection of F-Plasmid-Containing Escherichia coli Cells by Bacterial Virus T7 Is Determined by the Right End of T7 Gene 1

Phage T7 infects male (F-plasmid-carrying) Escherichia coli cells abortively, whereas the closely related phage T3 grows normally. The inability or ability of phage to replicate in male host cells depends on whether the right end of gene 1 (coding for the phage-specific RNA polymerase) consists of T7 or T3 DNA base sequences.     

Disturbance and contrasting patterns of population structure in the brachiopod Terebratulina septentrionalis (Couthouy) from two subtidal habitats

The population structures of Terebratulina septentrionalis (Couthouy) from exposed upper rock surface and semi-cryptic rock wall habitats at 33 m depth in the Gulf of Maine differ. Over a 3-yr period, population densities were consistently higher in rock wall habitats. Although both populations were dominated by juveniles (1–4 mm shell length), size-frequency distributions constructed from upper rock surface and rock wall populations were significantly different, as a result of a greater frequency of large brachiopods (> 20 mm shell length) in rock wall populations. Prominent modes occurred at 14–15 mm shell length in upper surface populations and at 19–20 mm length in rock wall populations. Recruitment was higher in rock wall habitats where ambient light intensities were significantly lower than on upper rock surfaces. Differences in recruitment are either the result of larval selection for shaded rock walls or differential juvenile mortality between habitats. The larvae of Terebratulina settle on a diverse array of substrata. These include bedrock, sandy polychaete tubes and algae in upper surface habitats and bedrock, calcareous polychaete tubes, and ascidians in rock wall habitats. Individuals attached to polychaete tubes and algae in upper surface habitats do not attain large body size (> 13 mm shell length). It is suggested that these differences in population structure reflect the greater intensity of disturbance in upper surface habitats. For example, the cod, Gadus morhua (Linnaeus), ingests brachiopods attached to algae and polychaete tubes in this habitat. Gastropod predation affects brachiopods in upper surface habitats but not in rock wall habitats. Predation by gastropods and asteroids is not size-specific. These results are consistent with the hypothesis that predation contributed to the decline in the abundance and diversity of articulate brachiopods since the Mesozoic, and suggest that the restriction of recent populations to semi-cryptic rock wall and crevice habitats is, in part, controlled by disturbance.     

Impedance of the electrogenic Cl− pump inAcetabularia: Electrical frequency entrainements,voltage-sensitivity,and reaction kinetic interpretation

Summary Reaction kinetic analysis of the electrical properties of the electrogenic Cl^– pump inAcetabularia has been extended from steady-state to nonsteady-state conditions: electrical frequency responses of theAcetabularia membrane have been measured over the range from 1 Hz to 10 kHz at transmembrane potential differences across the plasmalemma (V _m ) between –70 and –240 mV using voltage-clamp techniques. The results are well described by an electrical equivalent circuit with three parallel limbs: a conventional membrane capacitancec _m , a steadystate conductanceg _o (predominantly of the pump pathway plus a minor passive ion conductance) and a conductanceg _s in series with a capacitancec _p which are peculiar to the temporal behavior of the pump. The absolute values and voltage sensitivities of these four elements have been determined:c _m of about 8 mF m^–2 turned out to be voltage insensitive; it is considered to be normal.g _o is voltage sensitive and displays a peak of about 80 S m^–2 around –180 mV. Voltage sensitivity ofg _s could not be documented due to large scatter ofg _s (around 80 S m^–2).c _p behaved voltage sensitive with a notch of about 20 mF m^–2 around –180 mV, a peak of about 40 mF m^–2 at –120 mV and vanishing at –70 mV. When these data are compared with the predictions of nonsteady-state electrical properties of charge transport systems (U.-P. Hansen, J. Tittor, D. Gradmann, 1983,J. Membrane Biol. in press), model A (redistribution of states within the reaction cycle) consistently provides magnitude and voltage sensitivity of the elementsg _o ,g _s andc _p of the equivalent circuit, when known kinetic parameters of the pump are used for the calculations. This analysis results in a density of pump elements in theAcetabularia plasmalemma of about 50 nmol m^–2. The dominating rate constants for the redistribution of the individual states of the pump in the electric field turn out to be in the range of 500 sec^–1, under normal conditions.     

Alloantigen-specific cytotoxic and suppressor T lymphocytes are derived from phenotypically distinct precursors

Although Leu-2+ (OKT8+) T cells activated in the mixed lymphocyte reaction (MLR) mediate both alloantigen-specific cytotoxicity and suppression of alloantigen-induced proliferation, it is not known whether these functions derive from a single cell type or phenotypically distinct cells. This study was undertaken to examine the alloantigen-specific cytolytic and suppressor potential of two subpopulations of Leu-2+ cells distinguishable from one another on the basis of their binding to the monoclonal antibody 9.3. Leu-2+, 9.3+ and Leu-2+, 9.3- populations were purified from peripheral blood, cultured for 7 days with autologous helper/inducer (Leu-3+) cells and allogeneic non-T cells, and reisolated before testing for cytotoxicity and suppression. All detectable alloantigen-specific cytolytic activity was confined to the Leu-2+, 9.3+ subpopulation. Killing by this subset was specific for the HLA-A and B (class I) major histocompatibility complex (MHC) antigens of the priming cell. By contrast, suppression of proliferation was mediated predominantly by the Leu-2+, 9.3- cells, and suppression by this subpopulation was specific for the HLA-DR (class II) MHC antigens of the priming cell. The development of suppression by Leu-2+, 9.3- cells was unaffected by cyclosporin A (CsA), an agent shown previously to block the development of cytolytic but not suppressor cells in MLR. Alloactivated Leu-2+, 9.3+ cells were slightly inhibitory of fresh MLR, but this effect as well as the development of cytolytic cells was completely abrogated by CsA. These results indicate that suppressor and cytolytic Leu-2+ T cells activated in MLR are derived from distinct precursors separable by antibody 9.3.     

Differential recognition of the serologically defined HLA-A2 antigen by allogeneic cytotoxic T cells

A comprehensive analysis of human alloimmune cytotoxic T lymphocytes (CTLs) specific for the HLA-A2 antigen identified 11% of HLA-A2 positive cells as outliers. In total, 11 unrelated serologically indistinguishable, but distinguishable by cell-mediated lympholysis (CML) HLA-A2 positive outlier cells were identified. The outlier cells could be subdivided in two subgroups according to reactivity patterns obtained with CTLs directed against the HLA-A2 antigen of outlier cells and their inhibitory capacity in specific competitive inhibition experiments. Thus, the serologically defined HLA-A2 specificity can be divided into at least three subtypes using CTLs specific for the HLA-A2 antigen. Moreover, CTLs specific for an HLA-A2 subtype could be induced when responder cells expressed a different HLA-A2 subtype antigen. On the basis of several family studies, we conclude that the subtype HLA-A2 antigens are inherited in a codominant way.