Activation of yeast enolase by Cd(II)

Activation of yeast enolase by Cd2+ exhibits properties similar to activation by the physiological cofactor Mg2+. The activity is weakly stimulated, then inhibited by increasing ionic strength. The activity increases, then falls with increasing Cd2+ concentration. The effect of pH on activity produced by Cd2+ is very similar to that produced by Mg2+, except that the Cd2+ profile is shifted one pH unit to more alkaline values, and the maximum activity of the Cd2+-enzyme is about 10% of that of the Mg2+-enzyme. The apparent kinetic parameters of Cd2+ activation show little effect of pH except for inhibition by high concentrations of Cd2+: the apparent Ki increases sharply with pH. This is interpreted as the result of Cd2+ being a less effective "catalytic" metal ion, and Cd2+ being more effective in stabilizing the enzyme at alkaline pH's. The similarity of effects of ionic strength, divalent cation, and pH may be due to interaction with the same six sites per mole of enzyme. We also characterized the dependence of what is believed to be the enzyme-catalyzed enolization of a substrate analog, D-tartronate semialdehyde-2-phosphate (TSP) on similar parameters of pH, ionic strength, etc. The putative enolization is dependent on catalytic metal ion, although the TSP binds to the conformational Cd2+-enzyme complex. The reaction is very slow and very pH dependent, increasing with pH with a midpoint of reaction velocity at pH 8.7. There is a strong qualitative correlation between pH dependencies of reaction velocity of substrate conversion and TSP enolization and absorbance of the enzyme-bound TSP enolate, whether with Mg2+ or Cd2+ as cofactor. The slowness of the Cd2+-TSP reaction is not limited by proton release or any reaction involving covalent bonds to hydrogen. The apparent reaction rate constant increases linearly with Cd2+ concentration. Addition of excess ethylenediaminetetraacetic acid reverses the TSP reaction, but again very slowly. The binding of Cd2+ to the catalytic sites is characterized by low association and dissociation rate constants.     

The evolution of daily food sharing: A Bayesian phylogenetic analysis

Some human subsistence economies are characterized by extensive daily food sharing networks, which may buffer the risk of shortfalls and facilitate cooperative production and divisions of labor among households. Comparative studies of human food sharing can assess the generalizability of this theory across time, space, and diverse lifeways. Here we test several predictions about daily sharing norms–which presumably reflect realized cooperative behavior–in a globally representative sample of nonindustrial societies (the Standard Cross-Cultural Sample), while controlling for multiple sources of autocorrelation among societies using Bayesian multilevel models. Consistent with a risk-buffering function, we find that sharing is less likely in societies with alternative means of smoothing production and consumption such as animal husbandry, food storage, and external trade. Further, food sharing was tightly linked to labor sharing, indicating gains to cooperative production and perhaps divisions of labor. We found a small phylogenetic signal for food sharing (captured by a supertree of human populations based on genetic and linguistic data) that was mediated by food storage and social stratification. Food sharing norms reliably emerge as part of cooperative economies across time and space but are culled by innovations that facilitate self-reliant production.     

Neural crest origin of cardiac ganglion cells in the chick embryo: Identification and extirpation

Using interspecific grafting of neural crest between quail and chick embryos, it was determined that the cardiac ganglia originate from the cranial region (somites 1–2) of the vagal neural crest (somites 1–7). Neuronal uptake of [³H]choline was used as an index of neuronal development in the chick atrium. Normal uptake was found to be quite high between Days 8 and 14 of incubation. Following extirpation of neural crest over somites 1 to 3 at stages 8 to 10, neuronal uptake in 8-day chick atrium was decreased by 25–60% depending on the stage at which the lesion was performed. It is thought that the residual uptake represents preganglionic terminals from the dorsal motor nucleus of the vagus. Embryos with extirpations of neural crest over somites 1–3 performed at stage 9 showed the greatest decrease of neuronal choline uptake and did not live beyond 11 days of incubation. However, hearts from embryos with partial lesions (performed at stage 10) were treated on incubation Days 12 and 15 for demonstration of acetylcholinesterase in the subepicardial plexus. These hearts showed much less extensive neural plexus with sparse, small cardiac ganglia.     

The stomach contents of Patagonian toothfish around South Georgia (South Atlantic)

The proportion of Patagonian toothfish Dissostichus eleginoides , caught around South Georgia in the south-west Atlantic, with empty stomachs was much lower in fish caught in pots compared to longlines (28 and 91%, respectively, of examined individuals). It is hypothesized that pots caused reduced levels of stress on capture. Stomach content data examined from pot-caught fish will probably therefore be more comprehensive than that from fish caught using longlines. A wide range of prey items was identified in the stomachs of D. eleginoides and stomach contents of individuals caught using the two fishing methods were significantly different. The most common prey item for D. eleginoides caught using pots was the decapod prawn Nauticaris sp., which was restricted in location and depth. However, prawns were not common in the stomachs of D. eleginoides caught from the same location using longlines. Stomach contents from the two fishing methods remained significantly different when Nauticaris sp. were eliminated from the assessment, although fishes then dominated the diet of D. eleginoides caught using either fishing gear. The study confirms that D. eleginoides is an opportunistic carnivore, and indicates that feeding habits depend on the local availability of food items, as well as factors such as depth and predator size. The potential ecological impacts of fishing for D. eleginoides on the South Atlantic ecosystem are discussed.     

RELATIVE ABUNDANCE OF LARGE WHALES AROUND SOUTH GEORGIA (1979–1998)1

To assess large-whale stocks following the cessation of land-based South Georgia whaling in 1965, we report three independent sighting databases: a cruise in 1997, observations from Bird Island (NW of South Georgia) between 1979 and 1998, and mariner sightings between 1992 and 1997. All species were rare, with sightings of southern right whales being the most common event. Two right whales photographed off South Georgia matched animals known from Peninsula Valdés, Argentina, a population known to be growing at 7%per annum. In contrast, blue and fin whales appeared to be less abundant. A single blue whale mother-calf pair was observed off the Shag Rocks in February 1997. Extirpation of animals from this particular feeding ground is the most likely reason for ongoing low numbers of all species. Other factors may include competition for krill by traditional predators such as penguins and seals and more recently by humans, an unusually high rate of natural mortality, habitat change such as alteration in sea ice coverage, and/or the impact of ongoing whaling. The history of this critical area of large-whale habitat and this report demonstrate the need for improved, consistent longterm monitoring of population trends for these depleted stocks.     

Intertidal colonization rates. A matched latitude, north v. south, remote v. near shore island experiment

Colonization of artificial substrata was monitored on sheltered rocky shores at Husvik, South Georgia (54° 11'S; 36° 40'W) and Cumbrae, Scotland (55° 46'N; 4° 55'W) from mid summer to early autumn. South Georgia is a remote island (1,330 km from other land); Cumbrae is only 2 km from nearby coasts. Both islands were heavily glaciated for a period up to about 10,000 ybp, so the intertidal fauna is of geologically recent origin. The South Georgian fauna is depauperate and consists mainly of direct developers; that of Cumbrae is rich and largely larviparous. Colonization rates at Cumbrae were one to four orders of magnitude greater than at Husvik. It is suggested that the fauna of South Georgian shores stems from colonization by rafting from remote sources, while Cumbrae has been supplied predominantly by short-range pelagic larval dispersal. The measured differences in colonization rates reflect the substantial local advantage of larval dispersal over direct development in established communities.     

Early degranulation of human neutrophils: immunocytochemical studies of surface and intracellular phagocytic events.

Degranulation of azurophil and specific granules after phagocytic challenge with E. coli for 5 sec to 10 min was investigated in the human polymorphonuclear neutrophil (PMN). PMN were stained simultaneously with fluorescein and rhodamine-labeled monospecific antisera to myeloperoxidase (MPO) and lactoferrin (LF) to identify azurophil and specific granules, respectively, within single cells. Fixation was designed to preserve or disrupt differential permeability of cell membrane to fluorescent conjugates in order to study granule translocation. Within 5 sec after phagocytic challenge, MPO and LF appeared on the cell surface coating the bacteria as granule contents leaked from the incompletely formed phagolysosomes. The phagocytic cup, shown by scanning electron microscopy as large and circular, appeared by immunofluorescent markers to be outlined by curvilinear staining for both granule markers, and was always coincident with bacterial localization. MPO and LF appeared singly or simultaneously on the cell surface, suggesting that degranulation to the surface was random. Sequential phagocytic events were demonstrated by comparing staining intensities for each granule marker on the surface and intracellularly within single cells. LF sometimes appeared on the cell surface independent of the nascent phagosome, suggesting that perturbation of the cell membrane by bacteria may cause some specific granule extrusion not limited to the phagosome. These results imply that bacteria make contact with granule-associated anti-microbial substances within 5 sec after phagocytosis is initiated and that free communication of granule constituents occurs between the newly forming phagolysosome and the extracellular space.     

The Effect of Host Constitution on the Development of Plasmodium floridense*

More than 15,000 lizards from South Georgia were examined over a period of 16 years. Five percent of Sceloporus undulatus and 36% of Anolis carolinensis were found to harbor Plasmodium floridense. Development of 28 natural new infections was followed in detail as soon as they became patent and comparisons in the 2 host species made of intensity and duration of infections and of merozoite means during the periods of acute rise and decline. During the acute rise, the merozoite mean in Sceloporus was 10.6 ± 0.11 (8,495 segmenters counted), compared with 13.44 ± 0.15 in Anolis (3,805 counted); during the decline, the merozoite means were 8.55 ± 0.13 (3,305 counted) and 10.28 ± 0.09 (6,772 counted), respectively. It took an average of 150 (100–253) days for the infection to run its course in Sceloporus, compared with the average of 71 (60–90) days in Anolis; the peak of parasitemia in Sceloporus was 11,600 parasites/10,000 red cells, compared with 1,600 in Anolis. Both lizard genera produced 5–10% gametocytes.     

Carbon and nitrogen stable isotopic signatures of human dietary change in the Georgia Bight.

Measurement of carbon and nitrogen stable isotope ratios (delta 13C and delta 15N) in samples of human bone collagen (n = 93) from a temporal series of four prehistoric (early preagricultural, late preagricultural, early agricultural, late agricultural) and two historic (early contact, late contact) periods from the Georgia Bight, a continental embayment on the southeastern U.S. Atlantic coast, reveals a general temporal trend for less negative delta 13C values and less positive delta 15N values. This trend reflects a concomitant decrease in emphasis on marine resources and increased reliance on C4-based resources, especially maize. This dietary reorientation is most apparent for the early agricultural sample (AD 1150-1300), coinciding with the Mississippian fluorescence in the eastern United States. There is, however, a shift toward the use of C3 (non-maize) foods during the last prehistoric period (AD 1300-1450), which is likely related to environmental stress and social disruption. A heavier use of maize and terrestrial resources in general after the establishment of mission centers on barrier islands is indicated. A reduced dietary breadth during the mission period may have contributed to the extinction of these populations in the eighteenth century.     

A theory of charge separation,ion, electron and proton transport in photosynthetic membranes based on asymmetry of surface charges

We present a model for the light-induced charge separation, proton and ion transport across photosynthetic membranes based on an assumption of the transmembrane surface charge asymmetry. In dark equilibrium, this asymmetry gives rise to an internal membrane electric field whose direction is perpendicular to the membrane surfaces. The role of the field in the light-induced charge separation is similar to the function of the built-in electric field across a solid-state p-n junction. Light-generated free charge carriers in the membrane flow according to its direction and upon recombination on the surface give rise to an electrochemical potential difference for electrons across the membrane. The associated coupled electron-proton transport, and ion diffusion can be viewed as a response of the system to the light-induced redox and electric potential changes.