Phytoplankton population dynamics of a small reservoir: physical/biological coupling and the time scales of community change

This paper describes the day-to-day changes in species compositionthat resulted from intermittent wind mixing of the surface watersof a small reservoir. Two major scales of community change weredetected: a short-term (>1 day) scale associated with theredistribution of cells within the basin, and a 5–14-dayscale associated with growth responses. The physical scalesof change were found to be almost identical to the biologicalscales: wind stress caused changes in the temperature gradientof surface waters at scales of a day, and major vertical mixingevents occurred at scales of 10–14 days. The presenceof buoyant species ensured that rapid advection of populationsfollowed wind events. Community change was a function of bothadvection and growth, so that both real and apparent changesin abundance occurred. The observed seasonal succession wasboth a true succession and a changing sequence of populationsdependent on horizontal advection of water within the basin.Consistent stratification was present throughout the summerperiod and phytoplankton diversity was low. Even so, the seasonalsuccession was best described as a series of allogenic perturbationsfollowed by biological restructuring of the community. Dailysampling was necessary to document fully the mechanisms drivingthe seasonal succession of species.     

Mapping of human X-linked hypophosphataemic rickets by multilocus linkage analysis

Summary Eleven families with X-linked dominant hypophosphataemic rickets (HPDR) have been typed for a series of X chromosome markers. Linkage with probe 99.6 (DXS41) was demonstrated with a peak lod score of 4.82 at 10% recombination. Multilocus linkage analysis showed that HPDR maps distal to 99.6; this probe has previously been located at Xp22.31-p21.3 by in situ hybridisation. In the mouse hypophosphataemia (Hyp) maps to the distal part of the X chromosome; our location in man is consistent with a scheme which relates the mouse and human X chromosomes by two rearrangements. No marker has yet been found which shows no recombination with HPDR.     

Mechanisms of cytoskeletal regulation: functional and antigenic diversity in human erythrocyte and brain beta spectrin

A study of human erythrocyte and brain spectrin with particular emphasis on the beta subunits revealed a structural homology but functional dissimilarity between these two molecules. Six monoclonal antibodies raised to human erythrocyte beta spectrin identify three of the four proteolytically defined domains of erythrocyte beta spectrin. Five of these monoclonal antibodies cross-react with human brain spectrin. None of a previously identified set of alpha erythrocyte spectrin monoclonal antibodies [Yurchenco et al: J Biol Chem 257:9102, 1982] reacted with brain spectrin. A domain map generated by limited tryptic digestion shows that brain spectrin is composed of proteolytically resistant domains analogous to erythrocyte spectrin, but the brain protein is more basic. The binding of brain spectrin to erythrocyte ankyrin, both in solution and on erythrocyte IOVs, yielded an association constant approximately 100 time weaker than for erythrocyte spectrin. The binding of azido-calmodulin under native conditions was specific for the erythrocyte beta subunit but was not calcium dependent. In contrast, azido-calmodulin bound only to the alpha subunit of brain spectrin in a calcium-dependent manner. The similarity of structure but modified functional characteristics of the brain and erythrocyte beta spectrins suggest that these proteins serve different cellular roles.     

Ethics of predictive testing for Huntington's chorea: the need for more information.

The finding of a genetically linked polymorphic DNA marker has made possible a predictive test for Huntington''s chorea. This DNA probe has so far been used only for research and has technical limitations, but some workers now wish to apply it to clinical predictions. Those identified by the probe as being probable carriers of the Huntington''s chorea gene would be exposed to uncertain psychological risks and social pressures. Ethical guidelines should be established, but these require greater knowledge of the potential benefits and hazards of this powerful new procedure. Controlled clinical trials are urgently needed.     

Role of fructose 2,6-bisphosphate in the regulation of glycolysis and gluconeogenesis in chicken liver

Glucagon and dibutyryl cyclic AMP inhibited glucose utilization and lowered fructose 2,6-bisphosphate levels of hepatocytes prepared from fed chickens. Partially purified preparations of chicken liver 6-phosphofructo-1-kinase and fructose 1,6-bisphosphatase were activated and inhibited by fructose 2,6-bisphosphate, respectively. The sensitivities of these enzymes and the changes observed in fructose 2,6-bisphosphate levels are consistent with an important role for this allosteric effector in hormonal regulation of carbohydrate metabolism in chicken liver. In contrast, oleate inhibition of glucose utilization by chicken hepatocytes occurred without change in fructose, 2,6-bisphosphate levels. Likewise, pyruvate inhibition of lactate gluconeogenesis in chicken hepatocytes cannot be explained by changes in fructose 2,6-bisphosphate levels. Exogenous glucose caused a marked increase in fructose 2,6-bisphosphate content of hepatocytes from fasted but not fed birds. Both glucagon and lactate prevented this glucose effect. Fasted chicken hepatocytes responded to lower glucose concentrations than fasted rat hepatocytes, perhaps reflecting the species difference in hexokinase isozymes.     

An electron-spin-resonance spin-label study of the interaction of purified Mojave toxin with synaptosomal membranes from rat brain

The structural properties of isolated purified rat brain synaptosomal membranes, both in the presence and absence of purified active toxin of the Mojave snake Crotalus scutulatus scutulatus, were studied by spin-label electron spin resonance techniques. The spectra from eight different positional isomers of nitroxide-labelled stearic acids, a rigid steroid androstanol, and a spin-labelled phosphatidylcholine intercalated into the synaptosomal membranes, were obtained as a function of temperature from 4-40 degrees C. The flexibility gradient (from spin-label order parameters) and polarity profile (from isotropic splitting factors) across the synaptosomal membranes, was characteristic for lipid bilayers. The nitroxide spin-labelled steroid, androstanol, intercalated into the synaptosomal membrane, revealed the abrupt onset of rapid cooperative rotation about the long axis of the molecule at 12 degrees C showing that the lipid molecules are rotating rapidly around their long axes at physiological temperatures. The presence of the Mojave toxin affected the synaptosomal membrane in a complex manner, depending upon the temperature and the position of the nitroxide label on the alkyl chain of the stearic acid probe. Mojave toxin exerted little effect on the flexibility gradient of the synaptosomal membrane at 20 degrees C, a temperature at which the acyl chain labels detected a structural change in the membranes. At temperatures lower than 20 degrees C, the Mojave toxin produced a change in the flexibility gradient of the synaptosomal membrane which indicated an increased disordering in the upper region of the membrane and a concomitant increased ordering of the acyl chains in the deeper regions of the membrane. At temperatures higher than 20 degrees C, the order profile of the synaptosomal membrane was shifted by the presence of the Mojave toxin in a manner which indicated that the outer parts of the membrane were more rigid and the inner regions more fluid, than in controls. A cross-over point for the perturbation occurred at C8-9, which is about 12-14 A into the membrane. This is the approximate depth of the hydrophobic pocket shown in pancreatic phospholipase A2 [Drenth et al. (1976) Nature (Lond.) 264, 373-377], a protein likely to be homologous to the basic subunit of the toxin. At all temperatures, rotational lipid motion was inhibited by the toxin as indicated by the steroid probe. The electron spin-resonance spin-label results are interpreted in terms of the partial penetration of the basic subunit of the intact toxin into the membrane, disordering the ordered chains at low temperature and ordering the disordered chains at physiological temperatures. The purified individual toxin subunits did not perturb the membrane lipids at physiological temperatures implying that both subunits must be associated for activity of the toxin which is confirmed by toxicity studies.     

Application of a noninhibitory growth model to predict the transient response in a chemostat

A method of adapting a kinetic model based on steady-state chemostat data to predict the transient performance of a chemostat culture is presented. The proposal provides for a time delay which can be considered equivalent to a period of reduced activity of the organism subsequent to the introduction of a step change in operating conditions. The adapted kinetic model gives substantially better performance in predicting the transient response of an experimental system than the unmodified kinetic model.     

Ovostatin: a novel proteinase inhibitor from chicken egg white. I. Purification, physicochemical properties, and tissue distribution of ovostatin

A proteinase inhibitor which has strong anti-collagenase activity was found in chicken egg white. The inhibitor (pI = 4.9) was purified by poly(ethylene glycol) (5.5-10%) precipitation and chromatography on Ultrogel AcA 34, DEAE-cellulose, and Sephacryl S-300. The final product was homogeneous on 5% polyacrylamide gel electrophoresis. Stoichiometric inhibition was observed with the inhibitor and rabbit synovial collagenase and thermolysin (1:1 molar ratio with thermolysin). The inhibitor ran on sodium dodecyl sulfate-gel electrophoresis with reduction as a single protein band of Mr = 165,000. The molecular weight of the native inhibitor was estimated to be 780,000 by sedimentation equilibrium centrifugation. Centrifugation analysis in 6 M guanidine hydrochloride and of the reduced sample gave M omega = 380,000 and M omega = 195,000, respectively, where M omega is the weight-average molecular weight determined by equilibrium ultra-centrifugation. The results indicated that the inhibitor molecule is a tetramer of identical subunits linked in pairs by disulfide bonds. Since the molecular weight and the quaternary structure of the inhibitor were similar to those of alpha 2-macroglobulin (alpha 2M) in plasma, chicken alpha 2M was isolated and compared with the inhibitor. The inhibitor was not sensitive to methylamine, whereas chicken alpha 2M was. No immunocross-reactivity was observed between the inhibitor and chicken alpha 2M. The NH2-terminal sequence of the egg white inhibitor is Lys-Glu-Pro-Glu-Pro-Gln-Tyr-Val-Leu-Met-Val-Pro-Ala. The sequence of chicken alpha 2M is Ser-Thr-Val-Thr-Glu-Pro-Gln-Tyr-Met-Val-Leu-Leu-Pro-Phe. Considerable homology was found between the two sequences and to the NH2-terminal sequence of human alpha 2M. Monospecific antibody raised against the egg white inhibitor was employed to examine the tissue distribution of the inhibitor. The inhibitor was found only in oviduct and egg white, but not in other tissues or serum of chickens.     

Bleomycin treatment of chick fibroblasts causes an increase of polysomal type I procollagen mRNAs. Reversal of the bleomycin effect by dexamethasone

Bleomycin treatment of primary chick skin fibroblasts and chick lung fibroblasts resulted in a selective dose-dependent increase of cell layer procollagen synthesis. Solid support hybridization of total cellular RNA to 32P-labeled pro-alpha 1(I) and pro-alpha 2(I) cDNAs did not indicate an increase of total cellular procollagen type I mRNAs in bleomycin-treated cells. However, bleomycin treatment of chick skin fibroblasts causes a redistribution of procollagen type I mRNAs within the nuclear, cytoplasmic, and polysomal subcellular fractions. Both the nuclear and cytoplasmic procollagen type I mRNAs are significantly decreased in concentration after bleomycin administration. In contrast, the polysomal procollagen type I mRNAs are significantly increased in both chick skin and lung fibroblasts treated with bleomycin. Administration of dexamethasone to bleomycin-treated fibroblasts resulted in a reversal of the bleomycin-induced increase in cell layer procollagen synthesis. The increased amounts of polysomal procollagen type I mRNAs in bleomycin-treated cells were also reduced by subsequent administration of dexamethasone. These data indicate that bleomycin treatment of chick skin and chick lung fibroblasts results in a specific increase in procollagen synthesis in the cell layer which is mediated by elevated levels of polysomal type I procollagen mRNAs via a repartitioning of these mRNAs within the fibroblast. Furthermore, dexamethasone reverses the bleomycin-induced elevations of both cell layer procollagen synthesis and polysomal type I procollagen mRNAs.     

A Comparison of Pigment-Protein Complexes among Normal, Chlorophyll-Deficient and Senescent Soybean Genotypes

Pigment-protein complexes were isolated from chloroplasts of normal green and several types of chlorophyll-deficient soybeans. The complexes were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and comparisons were made between normal and chlorophyll-deficient genotypes of the relative amounts of chlorophyll associated with Photosystem I (PSI), Photosystem II (PSII), light-harvesting, and free pigment complexes.

Chlorophyll-deficient genotypes, compared to normal green genotypes, have fewer light-harvesting complexes and a higher ratio of PSII to PSI complexes. Chlorophyll associated with PSII in yellow genotypes is in relatively higher amounts in spite of the fact that these genotypes have much less grana stacking than normal green genotypes. Although PSII activity has been associated with appressed regions of grana in normal plants, our work shows that the association does not always hold true.