Oxidative activity of poikilotherm mitochondria as a function of temperature

In Newell & Northcroft (1967) evidence was presented which showed that the metabolism of certain intertidal invertebrates at rest does not vary greatly with temperature change. The following work was undertaken to determine whether temperature-independent metabolism could be demonstrated in suspensions of mitochondria extracted from poikilotherm tissue and whether it could be inferred that there was any difference in the ability of poikilotherms from different habitats to adjust toshort-term temperature change.
It was found that the rate of reaction/temperature curve of mitochondria isolated from the skate Raia had a flattened region below 10°C but above this the rate of oxidation of succinate and pyruvate increased regularly with temperature. The curve for intertidal forms had a gradual slope extending as high as 20°C in the mussel Mytilus edulis while in the terrestrial snail Helix aspersa the gradual slope reached 27.5°C after which the rate of oxidation of substrate increased sharply before declining towards higher temperatures. Finally, the curve for mitochondria isolated from the desert locust Schistocerca gregaria showed a gradual slope up to 35°C after which a sharp increase in the rate of oxidation of substrate occurred. Thus the extent of the gradual slope corresponds with the normal environmental temperature range to which the tissues of the poikilotherms are subjected and the general form of the R-T curve is such that rapid fluctuations within the normal environmental temperature range have relatively little effect on the rate of mitochondrial activity.     

Changes in cell surface glycoproteins during Dictyostelium development analysed using monoclonal antibodies

We have produced a series of monoclonal antibodies that recognize carbohydrate epitopes on cell surface glycoproteins of developing amoebae of Dictyostelium discoideum. The antibodies were found to have differential specificity for amoebae at different stages of development and were classified into types A to E on the basis of their temporal pattern of reactivity with the developing amoebal cell surface. Evidence from Western Blots and digestion of the glycoproteins with alkaline phosphatase were consistent with previous reports that the cell surface glycoproteins are extensively processed during development, leading at 16 h of development to the exposure of a highly antigenic core recognized by antibodies in group E. The nature of this core structure is indicated by the finding that antibodies in group E were found also to bind with high avidity to the plant glycoprotein horse radish peroxidase.     

The brain organization of butterflyfishes

Synopsis The encephalization indices of angelfishes (Pomacanthidae) and butterflyfishes (Chaetodontidae) are typical of advanced perciform fishes: both families lie in the upper part of the polygon of teleost indices. The chaetodontids seem to be a little more encephalized than pomacanthids. The general morphology of the brains in both families is very similar: small olfactory bulbs, large optic tectum and a cerebellum which covers the brain structures in front of it like a cap. This morphology is shared by another family of the coral reef biotope, the Acanthuridae. The histological architecture is also typical of advanced teleosts, with a cortex-like pallium, a laminated nucleus geniculatus (= pretectalis superficialis), a complex valvula cerebelli and a corpus glomerulosum with a clear neuropile centre. The quantitative analysis of the main subdivisions of the brain, either from relative volumes or from indices, shows small olfactory bulbs (microsmy) but important telencephalic and diencephalic centres, large tectal centres (vision) and large cerebellum (precise locomotion). Many of these peculiarities are shared by other fishes inhabiting coral reefs. The differences between the two families seem to be primarily correlated with food habits: the angelfishes, which are sponge-feeders and may have an overweight due to the ballast of the sponge-skeleton in their digestive tract, and which do not need either such good vision or such precise locomotion to pick up their prey, could be a little less encephalized than the butterflyfishes.     

Antibody-directed fibrinolysis. An antibody specific for both fibrin and tissue plasminogen activator

An investigation was made to determine whether it is possible to attract tissue plasminogen activator (tPA) to the site of a thrombus by means of an antibody with affinites for both tPA and fibrin. A bispecific antibody conjugate was constructed by cross-linking two monoclonal antibodies: one specific for tPA, the other specific for fibrin. The bispecific antibody enhanced fibrinolysis by capturing tPA at the site of a fibrin deposit. In an in vitro quantitative fibrinolysis assay, the relative fibrinolytic potency of tPA bound to the bispecific antibody was 13 times greater than that of tPA and 200 times greater than that of urokinase. When fibrin was treated with the bispecific antibody before being mixed with tPA, the relative fibrinolytic potency of tPA was enhanced 14-fold. This capture also occurred when the concentration of tPA present in the assay was less than the concentration of tPA present in normal human plasma. In a human plasma clot assay, samples containing both the bispecific antibody and tPA exhibited significantly more lysis than did samples containing tPA alone. In spite of the increased clot lysis effected by the presence of bispecific antibody, there was no significant increase in fibrinogen or alpha 2-antiplasmin degradation at equal tPA concentrations. The ability of the bispecific antibody to concentrate exogenous tPA in vivo was then examined in the rabbit jugular vein model. Systemic infusion of a small amount of tPA (10,000 units) produced no significant increment in thrombolysis over the level of spontaneous lysis (14 +/- 8%). However, the simultaneous infusion of 10,000 units of tPA and 2 mg of bispecific antibody resulted in 42 +/- 14% (p less than 0.01) lysis. These results suggest that a molecule capable of binding both fibrin and tPA with high affinity could enhance thrombolysis in the circulation by capturing endogenous tPA.     

Adenosine receptors are expressed during differentiation of monocytes to macrophages in vitro. Implications for regulation of phagocytosis

Ingestion by phagocytes is known to be markedly enhanced by physiologic signals such as cytokines and extracellular matrix proteins which may be found in inflammatory sites. Little investigation has been made of mechanisms that may depress this increased rate of phagocytosis during resolution of inflammation. We show that adenosine can act as an inhibitor of phagocytosis by macrophages derived from in vitro culture of human peripheral blood monocytes. Adenosine (Ado) is equally effective at inhibiting IgG Fc and complement-mediated phagocytosis. However, Ado has no effect on phagocytosis by freshly isolated monocytes. Inhibition by Ado begins after 2 days in culture and reaches a plateau by 5 days; these kinetics of induction of inhibition of phagocytosis parallel an increase in specific Ado binding to the macrophage plasma membrane. Ado binds to cultured monocytes with a Kd of 6 microM. This affinity and the observation that 2-chloroadenosine and 5'-N-ethylcarboxamidadenosine are the most potent inhibitors of phagocytosis suggest that the Ado receptors expressed during monocyte differentiation are of the A2 type. The inhibition of phagocytosis may be mediated by cAMP, a second messenger coupled to A2 receptors in several cell types. Thus, plasma membrane expression of A2 receptors dramatically increases during monocyte differentiation in vitro. These data show that a potentially physiologic mediator can have very different effects on the function of monocytes and macrophages. This suggests a mechanism whereby phagocytic function at inflammatory sites can be down-regulated if and only if signals for the recruitment of new phagocytes have subsided.     

Effect of lysophosphatidylcholine on the NADH-ferricyanide reductase activity associated with the plasma membranes of corn roots

Plasma membranes from corn roots (Zea mays L.) were isolated by aqueous two-phase partitioning. A fraction enriched in a vanadate-sensitive ATPase showed characteristics of a plasma membrane ATPase. The sidedness of these vesicles was 89% right-side-out, as evaluated by the ATPase latency. A NADH-ferricyanide reductase was associated with these plasma membrane vesicles. The rate of ferricyanide reduction was 1.3 μmol · min⁻¹·mg⁻¹ protein and was strongly enhanced by the addition of lysophosphatidylcholine (LPC). The effect of this detergent on membrane solubilization and reductase activity was particularly studied. This type of detergent treatment revealed two pH optima (7.0 and 5.0) for the reductase activity, which exhibited biphasic kinetics in the absence or presence of the detergent. These data suggest that two or more reductases could be involved. In addition, membrane vesicle solubilization and determination of ATPase and reductase latency were simultanously studied. From these experiments, it is postulated that the reductase, which exhibits an optimum pH at 7.0 and is slightly stimulated by LPC, could be located on the external side of the plasmalemma. In contrast, the reductase at pH 5.0 strongly stimulated by the detergent treatment, is probably located on the internal side of the membrane, such as the catalytic site of ATPase. Finally, a possible direct action of LPC on the enzymes, is discussed.     

Misting and nitrogen fertilization of shoots of a saltmarsh grass: effects upon fungal decay of leaf blades

We conducted a 12-week field manipulation experiment in which we raised the nitrogen availability (ammonium sulfate fertilization to roots) and/or water potential (freshwater misting) of decaying leaf blades of a saltmarsh grass (smooth cordgrass, Spartina alterniflora) in triplicate 11-m² plots, and compared the manipulated plots to unmanipulated, control plots. The ascomycetous fungi that dominate cordgrass leaf decomposition processes under natural conditions exhibited a boosting (>2-fold) of living standing crop (ergosterol content) by misting at the 1 st week after tagging of senescent leaves, but afterwards, living-fungal standing crop on misted blades was equivalent to that on control blades, confirming prior evidence that Spartina fungi are well adapted to natural, irregular wetting. Misting also caused 2-fold sharper temporal declines than control in instantaneous rates of fungal production (ergosterol synthesis), 5-fold declines in density of sexual reproductive structures that were not shown by controls, and 2-fold higher rates of loss of plant organic mass. Extra nitrogen gave a long-term boost to living-fungal standing crop (about 2-fold at 12 weeks), which was also reflected in rates of fungal production at 4 weeks, suggesting that saltmarsh fungal production is nitrogen-limited. Although bacterial and green-microalgal crops were boosted by manipulations of nitrogen and/or water, their maximal crops remained 0.3 or 2% (bacteria or green microalgae, respectively) of contemporaneous living-fungal crop. The fungal carbon-productivity values obtained, in conjunction with rates of loss of plant carbon, hinted that fungal yield can be high (>50%), and that it is boosted by high availability of nitrogen. We speculate that one partial cause of high fungal yield could be subsidy of fungal growth by dissolved organic carbon from outside decomposing leaves.     

Ecomethodology for organoosmotrophs: Prokaryotic unicellular versus eukaryotic mycelial

Although they are very unlikely to play large direct roles in water-column microbial loops, eukaryotic mycelial decomposers (the mycelial true fungi, eumycotes, and zoosporic fungi, oomycotes) have the potential to be important secondary producers in decaying plant material in shallow aquatic systems. Their secondary productivity may lead to important exchanges of material with microbial loops: output of ascospores, conidia, zoosporic flagellates, leaked lysates, and particles of decayed plants containing mycelium; input of dissolved organics and inorganic nutrients. Development of methods for ecological study of the aquatic mycelial eukaryotic decomposers has not advanced as rapidly as that for the prokaryotes of microbial loops, probably because (1) there are fewer aquatic microbial ecologists with mycological training and inclination than with prokaryotic leanings; and (2) the mycelial decomposers are difficult to work with, because they produce their mycelial mass virtually entirely within opaque solid substrates. Direct microscopic methods have emerged as prime tools for the measurement of prokaryotic mass, whereas an index-chemical assay (ergosterol) is currently the most efficient way to measure the mass of eumycotes. For measuring productivity of prokaryotes of microbial loops, microbial ecologists may choose from several (>10) published and field-tested methods, involving direct microscopy or monitoring of radiotracers. Extensive reviews of distribution and dynamics of aquatic bacterial mass and productivity have appeared. For measuring productivity of eukaryotic mycelial decomposers, one has only two published methods from which to choose, a direct-microscopic and a radiotracer method, neither of which has had adequate field testing. We are, furthermore, much less well equipped to obtain mass and productivity information for the poorly known mycelial oomycotes than we are for the eumycotes. Application of productivity techniques and nucleic-acid technology, may within the next decade allow knowledge of ecology of aquatic eukaryotic mycelial decomposers to advance to levels approaching that for the prokaryotes of microbial loops.     

Relation between infection with Helicobacter pylori and living conditions in childhood: evidence for person to person transmission in early life.

OBJECTIVES--To relate the prevalence of infection with Helicobacter pylori in adults to their living conditions in childhood to identify risk factors for infection. DESIGN--Prevalence study of IgG antibodies to H pylori (> 10 micrograms IgG/ml, determined by enzyme linked immunosorbent assay (ELISA)) and reported living conditions and other socioeconomic factors in childhood. SETTING--Three factories in Stoke on Trent. SUBJECTS--471 male volunteers aged 18 to 65 years. MAIN OUTCOME MEASURES--Seroprevalence and variables in childhood. RESULTS--Seroprevalence of H pylori increased with age (22/74 (29.7%) at < 30 years v 29/46 (63%) at 55-65 years; P < 0.001 for trend) and was related to manual occupation (14/65 (21.5%) for non-manual v 162/406 (39.9%) for manual; P = 0.003). After data were adjusted for age and occupation subjects from large families, whose childhood homes were crowded or who regularly shared a bed in childhood, were significantly more likely to be seropositive (adjusted odds ratio (95% confidence interval) 2.15 (1.41 to 3.30) for crowding and 2.13 (1.38 to 3.30) for sharing a bed), but there was no relation with possession of a bathroom, inside toilet, refrigerator, or household pets in childhood. CONCLUSIONS--Close person to person contact in childhood is an important determinant of seroprevalence of H pylori in adulthood, suggesting that the infection is transmitted directly from one person to another and may be commonly acquired in early life.     

Metabolite effectors for short-term nitrogen-dependent enhancement of phosphoenolpyruvate carboxylase activity and decrease of net sucrose synthesis in wheat leaves

It has been demonstrated previously that field pea (Pisum sativum L. cv. Express) grown in hydroponic culture on a complete nutrient solution with low NH₄⁺ concentrations (<0.5 mM) will produce a larger than normal proliferation of nodules. Peas grown in the absence of mineral N in hydroponic culture have been shown to rapidly autoregulate nodulation, forming a static nodule number by 14 to 21 days after planting. The present study further characterizes the effect of NH₄⁺ concentration in hydroponic culture on nodulation and nodule growth. Peas were grown continually for 4 weeks at NH₄⁺ concentrations that were autoregulatory (0.0 mM), stimulatory (0.2 mM) or inhibitory (1.0 mM), or peas were transferred between autoregulatory or NH₄⁺ inhibited and stimulatory solutions after 2 weeks. The peas nodulated as expected when grown under constant autoregulatory, stimulatory or inhibitory concentrations of NH₄⁺. When peas were transferred from the inhibitory (1.0 mM) to the stimulatory solution (0.2 mM) a massive proliferation of nodule primordia over the entire root system was observed within 3 days of the transfer. When they were transferred from the autoregulatory (0.0 mM) to the stimulatory (0.2 mM) solution a 10-day delay occurred before a proliferation in nodule primordia occurred at distal regions of the root system. These findings support our hypothesis that low concentrations (<1.0 mM) of NH₄⁺ in hydroponic culture cause a suppression of autoregulation in pea. In addition, the temporal and spatial differences in nodule proliferation between transfer treatments demonstrate at a whole plant level that autoregulation and NH₄⁺ inhibition suppress early nodule development via different mechanisms.