Orientation and ingestion rates of larval Anopheles albimanus in response to floating particles

Response of fourth-instar larvae of Anopheles albimanus Wiedemann (Diptera: Culicidae) to food and inert particles floating at the water surface was studied. In a choice test, larvae aggregated at powdered organic materials (blood meal, liver powder alfalfa flour and wheat flour) but not at inert materials (kaolin, chalk or charcoal). Larvae responded positively to proteins as well as some carbohydrates, but not to cellulose. Retention of larvae at food sources found by random locomotion was found to be responsible for larval aggregation. Larvae ingested food particles 6–9 times faster than insert particles. The significance of Anopheline feeding behavior in the development of formulations of stomach toxins (bacterial agents) used in larval control is discussed.

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Zusammenfassung Die vorliegende Studie befasst sich mit Verhaltensreaktionen von Anopheles albimanus Viertlarven auf an der Wasseroberfläche schwimmende Partikel. Verteilung und Orientierung der Larven wurde in einer Wahlapparatur quantifiziert. Nach Auftrag von Alfalfamehl, Weizenmehl, Stärke, Blutmehl, Leberpulver und Fischmehl wurde Aggregation der Larven in den beköderten Fächern der Apparatur beobachtet. Sowohl Proteine (Casein) als auch einige Kohlehydrate (Amylose, Amylopectin) lösten Aggregationen der Larven aus. Im Unterschied dazu führte Auftrag von Kreide, Kaolin, Polyaethylenpulver, Talcum oder Cellulose nicht zu Aggregationen. Zur Beschreibung der Entstehung larvaler Aggregationen bei Futterstoffen wurden die Schwimmbewegungen der Larven in Anwesenheit von Weizenmehl als Ködersubstanz quantifiziert. Da keine Attraktion der Larven im Sinne einer gerichteten Schwimmbewegung beobachtet werden konnte, wird geschlussfolgert, dass sofortige Beendung der Suchaktivität der Larven bei zufällig gefundenen Futterquellen für die beobachteten Aggregationen bei organischen Substanzen verantwortlich ist.Die Fressraten der Larven bei Angebot verschiedener Substanzen im Überschuss wurde bestimmt. Larven fülten drei von insgesamt sechs Darmabschnitten innerhalb von 15–30 min bei Angebot von Futtersubstanzen, während die Füllung von nur zwei Darmabschnitten mit inerten Materialien erst nach 90–120 min zu beobachten war. Die Resultate werden in Bezug auf wasseroberflächengebundene Formulierungen von Frassgiften diskutiert. Inerte Trägersubstanzen werden wahrscheinlich wesentlich langsamer aufgenommen als Futtersubstanzen. Da An. albimanus Larven nicht von Futterquellen angezogen werden, ist eine rasche und wirksame Giftaufnahme besonders dann zu erwarten, wenn die gesamte Oberfläche der Brutgewässer mit toxinhaltigen Trägerpartikeln bedeckt werden kann.

     

The Thatcher illusion in humans and monkeys

Primates possess the remarkable ability to differentiate faces of group members and to extract relevant information about the individual directly from the face. Recognition of conspecific faces is achieved by means of holistic processing, i.e. the processing of the face as an unparsed, perceptual whole, rather than as the collection of independent features (part-based processing). The most striking example of holistic processing is the Thatcher illusion. Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 180°), but strikingly grotesque when the face is upright. This effect can be explained by a lack of processing capabilities for locally rotated facial features when the face is turned upside down. Recently, a Thatcher illusion was described in the macaque monkey analogous to that known from human investigations. Using a habituation paradigm combined with eye tracking, we address the critical follow-up questions raised in the aforementioned study to show the Thatcher illusion as a function of the observer''s species (humans and macaques), the stimulus'' species (humans and macaques) and the level of perceptual expertise (novice, expert).     

The cytomegalovirus enhancer: a pan-active control element in transgenic mice.

In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney.     

The light organ symbiont Vibrio fischeri possesses two distinct secreted ADP-ribosyltransferases.

We have previously described the purification, cloning, and initial characterization of a secreted ADP-ribosyltransferase, halovibrin (gene designation hvn), from the luminescent light organ symbiont Vibrio fischeri. This report describes a strategy for overexpression of halovibrin, the production and refinement of antihalo-vibrin antisera, and the molecular biological construction of a V. fischeri halovibrin null strain. Biochemical analysis of this mutant revealed that V. fischeri hvn null still possessed ADP-ribosyltransferase activity and that this activity is immunologically, genetically, and structurally distinct from the previously described enzyme. This unusual finding, of two ADP-ribosyltransferase enzymes produced by a microorganism, is complemented by the details of the purification to apparent homogeneity and in vitro regulation of this new protein, halovibrin-beta.     

Functional asymmetry of the F0 motor in bacterial ATP synthases

F₁F₀ ATP synthases use the electrochemical potential of H⁺ or Na⁺ across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F₀ parts of a Na⁺- and H⁺-dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of ∼100 times higher Na⁺ or H⁺ concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F₀ parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo . In Escherichia coli , we observed respiratory chain-driven ATP production at pH 7–8, while P -site pH values < 6.5 were required for ATP synthesis in vitro . This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface.     

Secondary conformational polymorphism of nucleic acids as a possible functional link between cellular parameters and DNA packaging processes

Circular dichroism and electron microscopy studies of various in vitro DNA packaging systems indicate that all the factors which induce and modulate the secondary conformation of DNA molecules are capable of eliciting nucleic acids condensation processes into tight, highly ordered tertiary structures as well as altering the extent of order and compactness within the resulting species. Specifically, such factors include the ionic strength, the presence of particular dehydrating agents and polyamines, as well as the pH values. It is proposed that slight alterations of these parameters induce the formation of short non-B-DNA segments that propagate as a perturbation along the B-DNA double helix. The structural fluctuations of the dsDNA molecules that result from the conformational discontinuities formed at the junction sites between the B motif and the conformationally altered segments alter the elastic response of the nucleic acids and facilitate cooperative condensation processes. Moreover, the type and frequency of the structurally modified clusters interspersed within the B conformation and determined by the environmental parameters are shown to provide a means for continuous regulation of the extent and mode of DNA packaging. The ionic strength and hydrophobic environment in the close vicinity of the DNA molecules are controlled and modulated in vivo by DNA-binding proteins such as histones and protamines; similarly, pH values and polyamine concentrations are constantly regulated in living systems. It is suggested, therefore, that the secondary structural polymorphism which characterizes the DNA molecules might display a regulatory role by acting as a functional link between cellular parameters and the extent, mode, and timing of nucleic acid packaging processes.     

Specific inactivation of hepatic fatty acid hydroxylases by acetylenic fatty acids

The terminal acetylenic analogue of lauric acid, 11-dodecynoic acid (11-DDYA), specifically inactivates hepatic cytochrome P-450 enzymes that catalyze omega- and omega-1-hydroxylation of lauric acid. The inactivation, as required for a suicidal process, is NADPH- and time-dependent and follows pseudo-first order kinetics. In contrast, 11-DDYA causes no measurable change in the spectroscopically-measured concentration of cytochrome P-450 or in the N-demethylation of benzphetamine or N-methyl p-chloroaniline. 10-Undecynoic acid is as effective a suicide substrate for fatty acid hydroxylases as 11-DDYA but 11-dodecenoic acid is much less effective. 11-DDYA is able to completely inhibit omega-hydroxylation but suppresses no more than 50% of omega-1-hydroxylation despite the fact that both activities are completely inactivated by 1-aminobenzotriazole. At least three hepatic cytochrome P-450 fatty acid hydroxylases, one omega-hydroxylase and two omega-1-hydroxylases, are required by these results. The construction of suicide substrates that specifically inactivate cytochrome P-450 fatty acid hydroxylases provides a new experimental probe of the physiological role of this process.     

An inhibitor of plasminogen activation from human placenta. Purification and characterization

Placental extracts contain inhibitors of human urinary urokinase. These extracts form a heterogeneous population of complexes with 125I-urokinase that are recognizable by changes in gel filtration profile and mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment with reducing agents eliminated the size heterogeneity without loss of activity, thereby allowing the placental inhibitor to be purified. Active inhibitor has been isolated in apparently homogeneous form after an eight-step procedure that included salt extraction, ammonium sulfate fractionation, column chromatography on CM-cellulose, DEAE-Sepharose, and hydroxylapatite, chromatofocusing, preparative gel electrophoresis, and hydrophobic chromatography. The purified inhibitor has Mr = 47,000. The inhibitor is relatively specific for plasminogen activators since it does not inhibit the action of plasmin, factor XIIa, plasma kallikrein, or thrombin. The inhibitor forms complexes with 1:1 stoichiometry that block the active sites of urokinase (but not prourokinase) and both one- and two-chain forms of tissue plasminogen activator. The stability of these complexes in sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggest that they are based on covalently bonded structures. Although both types of plasminogen activator are inhibited, the rate of interaction is significantly faster with urokinase, tissue plasminogen activator being inhibited less efficiently. The complexes formed can be dissociated by mild alkali or hydroxylamine, thereby regenerating both enzymes and inhibitor at their original molecular weights. The results suggest that the complexes are stabilized by ester-like bonds; these might involve the hydroxyl of serine at the active site of the proteases and a carboxyl group in the inhibitor.