Hydrogen-ion titration curve of ovomucoid.

A systematic study of the H+ titration curve of purified ovomucoid was made at three temperatures (15, 25 and 35 degrees C) and three ionic strengths (0.05, 0.15 and 1.0). In all, 49 protons were dissociated reversibly in the pH range, 2.0-12.0. From the analysis of the results up to pH 12.0, the numbers of different dissociable groups per 28 300 g protein, together with their intrinsic pK values in parentheses were found tp be' 27 sode-chain carboxyl (pKint=4.0), four imidazole (pKint=6.5), one alpha-amino (pKint=7.5), 12 epsilon-amino (pKint=9.6), one guanidino (pKint=11.8) and one alpha-carboxyl group with abnormally low pK. The total number of basic nitrogens per mole of the protein was 22 so that four guanidino groups remained untitrated up to pH 12.0. Spectrophotometric titration showed that three out of five phenolic groups were titrated reversibly up to pH 11.9 with an intrinsic pK of 10.25; the remaining two groups became accessible only on protein denaturation. Viscosity results suggested absence of conformational change in the pH range 2.0-11.2. This explains the constancy of the pK values of carboxyl groups in the pH range 2.0-5.0. The empirical value of the electrostatic interaction factor, w, was 0.04, both in the carboxyl and phenolic regions.     

Mixed gelation theory. Kinetics, equilibrium and gel incorporation in sickle hemoglobin mixtures.

This paper outlines a theoretical formalism for describing the gelling behavior of sickle cell hemoglobin in mixtures with other hemoglobin and non-hemoglobin proteins. Experimental applications are reported for hybridized and unhybridized mixtures of HbS (sickle hemoglobin), HbA (adult hemoglobin), HbF (fetal hemoglobin), and HbC Harlem. The theory is a general one based on a modification of the sol—gel phase equilibrium equation to take into account the varying tendencies of different hemoglobin species to promote gelation, and specific hemoglobin interactions are encoded in gelling coefficients which quantify gelling capability. Gelling coefficients for the hemoglobin species dealt with here are evaluated by measuring incorporation into the polymer phase in S-A, S-F, and S-C_H mixtures. Given this information, the theory is found to provide accurate prodictions for the equilibrium gelling behavior of the calibrating pairs themselves when they are hybridized or unhybridized, for gelation kinetics in diverse mixtures of these species taken two, three and four at a time, for the anomalous equilibrium and kinetic gelling behavior of A- C_H mixtures, and it also accounts for a variety of results previously published by others. Apparently, given the gelling coefficients for any mutant hemoglobin, one can compute gelling behavior (equilibrium, kinetics, incorporation, etc.) in any specified mixture with any other known hemoglobin(s). The gelling coefficients for any mutant hemoglobin depend upon, and therefore provide information about, gel interactions at the mutant site. From the gelling coefficients one can also obtain the change in free energy of interaction in the gel due to the altered residue. Experimental approaches are described which allow an analysis for the gelling coefficients of any mutant hemoglobin to be performed in a few hours.     

The dissociation of human deoxyhemoglobin and mixed state hemoglobin into monomer.

The experimental hybridizations between fully deoxygenated human and canine hemoglobins and between half-ligated human hemoglobin and canine cyanomethemoglobin show that new two hybrids in addition to the parent hemoglobins were clearly formed in the mixtures at the high concentration of KI. Thus, human deoxyhemoglobin under the present conditions is in an equilibrium with three species, tetramer in equilibrium dimer in equilibrium monomer. This means that the deoxyhemoglobin is in R-T equilibrium, and shifts considerably toward the R state under the present conditions. On the other hand, the half-ligated hemoglobin in 1.5 M KI becomes much more dissociable than the deoxy T state and appears to be completely transformed into the R state. Nevertheless, the co-operativity, n, is still high (n = 2.0).     

Comparative Studies of NAD+-Dependent Maltose Dehydrogenase and d-Glucose Dehydrogenase Produced by Two Strains of Alkalophilic Corynebacterium Species

Glycinin was dialyzed against low ionic strength buffer (μ = 0.01) and centrifuged in sucrose density gradient. Two major components with the sizes of 7S and 1 IS were obtained. When each component was separately recentrifuged, the intrinsic peak of each was predominantly given. This indicates that there were two molecular species in the glycinin, one being dissociable and the other undissociable at low ionic strength. The dissociable species reversibly associated to the size of 11S at high ionic strength. The conformation of each species was different, the dissociable species being more random and unstable than the undissociable species at low ionic strength. The dissociable species contained more ASIV and less ASIII than the undissociable species.     

Some implications of a first-order model of inter-plant competition for the means and variances of complex mixtures

Summary Factorial models commonly used in the analysis of overall and component yields of binary mixtures of genotypes are generalised to include mixtures of any number of components (size, m) and the form of an analysis of variance for fitting such a model to tertiary mixtures is outlined. Such a model contains main effects and interactions up to the mth order, and is specific to the size of mixture so that no equivalence necessarily exists between similar parameter sets for different sized mixtures. Monocultures can be regarded as a special case of the general model.A simple model of intra-and inter-component competition is defined which assumes that plants do not interact in their competitive effects on others, a condition which is equivalent to an absence of second and higher order interactions in statistical analyses of mixtures of any size. Simple scaling tests involving the yields of components or whole mixtures of different sizes can also be used to test the adequacy of the model. This competition model least to a linear relationship between the mean yield of a mixture and the reciprocal of the number of components it contains, and thus allows the prediction of means and other statistical parameters for mixtures of one size from those of others.     

Mixed-gas model for predicting decompression sickness in rats.

A mixed-gas model for rats was developed to further explore the role of different gases in decompression and to provide a global model for possible future evaluation of its usefulness for human prediction. A Hill-equation dose-response model was fitted to over 5,000 rat dives by using the technique of maximum likelihood. These dives used various mixtures of He, N(2), Ar, and O(2) and had times at depth up to 2 h and varied decompression profiles. Results supported past findings, including 1) differences among the gases in decompression risk (He < N(2) < Ar) and exchange rate (He > Ar approximately N(2)), 2) significant decompression risk of O(2), and 3) increased risk of decompression sickness with heavier animals. New findings included asymmetrical gas exchange with gas washout often unexpectedly faster than uptake. Model success was demonstrated by the relatively small errors (and their random scatter) between model predictions and actual incidences. This mixed-gas model for prediction of decompression sickness in rats is the first such model for any animal species that covers such a broad range of gas mixtures and dive profiles.     

Effect of functional group richness and species richness in manipulated productivity–diversity studies: a glasshouse pot experiment

Species and functional group (grasses, legumes, creeping nonlegume forbs, rosette nonlegume forbs) richness of species assemblages composed of 16 species from four functional plant groups were manipulated to evaluate the productivity-diversity relationships in a greenhouse pot experiment. Pots were filled with sand, and supplied at two levels of nutrients. The plants were grown in monocultures, two, four, eight and 16 species mixtures. Individual two, four, and eight species mixtures differed in the richness of functional groups. Although the two characteristics of biodiversity, i.e. species and functional group richness, were necessarily correlated, it was shown that it is possible to separate their effect statistically, and also test for their common effect without pronounced loss of test power. There was a pronounced increase of average aboveground biomass and a mild increase in belowground biomass with biodiversity. The effect of functional group richness was more pronounced than the effect of the number of species. By using the method of Loreau and Hector (Nature 411 (2001) 72), selection and complementarity effects were statistically separated, and the overyielding index was calculated as a ratio of the productivity of a mixture to the productivity of its most productive component (to demonstrate transgressive overyielding). Positive values of complementarity and transgressive overyielding were both found, particularly in some rich communities and under high nutrient levels. Complementarity significantly increased only with functional group richness and mainly under high nutrients in the belowground biomass. Some species, when grown in monocultures, had decreased productivity under higher nutrients, and thus were more productive in mixtures than in monocultures. It seems that those species suffered from too high nutrient levels when grown in monocultures, but not in the presence of other species, which were able to use the nutrients in high concentrations and effectively decrease the nutrient levels. As a consequence, mixtures of high diversity were always more productive under high nutrients. The difference in species proportions between high and low nutrients, characterized by chord distance, increased with species richness. The relative change in productivity decreased with the number of functional groups. This suggests that species richness might lead to stabilization of aggregate characteristics (like total productivity) under changing environmental conditions by changing the proportions of individual species.     

Multiple choice: hemiparasite performance in multi‐species mixtures

Hemiparasitic plants have green leaves, but extract water and solutes from neighbouring plants. It is still poorly understood how different host plants in communities contribute to parasite performance, as species that are good hosts in single‐host experiments may not necessarily be preferred hosts in mixtures. We grew the root hemiparasite Rhinanthus alectorolophus (Orobanchaceae) together with each of 13 host species (experiment 1) and with 15 different four‐species mixtures of these hosts (experiment 2) that differed in the number of legumes and of host functional groups. Parasites profited from mixtures including more legumes and from mixtures including different host functional groups. Some host species and mixtures were very tolerant of parasitism and supported large parasites without being strongly suppressed in their own growth, but the suppression of a species in the single‐host experiment did not explain the suppression of a species in a host mixture. We thus calculated for each host species an index of the difference in suppression between the two experiments which may be related to host use in a mixture. Host quality (mean parasite biomass with a host species) in the single‐host experiment could explain 64% of the variation in parasite biomass with a host mixture when it was weighted by the proportion of the host species in the mixture without the parasite and by the suppression difference index. Our results suggest that plant species which are the best hosts in single‐host experiments are not always those used most strongly by a parasite growing with a mixture. Together with the finding that hemiparasites benefit from a mixed diet based on hosts from different functional groups this suggests that parasites prefer certain host species to obtain a mixed diet.     

Quantitative analysis of metabolic processes. II. A model-system for the synthesis of the dissociable enzyme and mathematical formulation of the process

Schemes are presented for induced synthesis of the dissociable enzyme in which repeated use of the template is made. The role of the inducer is to release the repression. A mathematical analysis is carried out and expressions are obtained to describe the kinetics of enzyme formation. A practical case (penicillinase synthesis) is compared with theoretically derived equations by using an analogue computer to simulate an enzyme forming system. A good correlation between theoretical and experimental data is obtained.     

Spiracanthus bovichthys n. gen. n. sp. (Acanthocephala: Arhythmacanthidae), a parasite of littoral fishes of the central south coast of Chile

A new acanthocephalan species, Spiracanthus bovichthys n. gen. n. sp., is described. Samples were taken from 26 marine fish species between 23 and 53 degrees S of Chile. The parasite was found in the intestine of 6 species and only between 36 and 40 degrees S, especially in those fish that prey on small crustaceans in the upper and sublittoral zone. The parasite was found in Bovichthys chilensis (Reagan). Auchenionchus variolosus (Valenciennes), Calliclinus genigutattus (Valenciennes), Sindoscopus australis (Fowler and Bean), Myxodes cristatus Valenciennes, and Gobiesox marmoratus (Jenyns). However, only the first species is a suitable host for the parasite as evidenced by the presence of mature females. This acanthocephalan belongs to Arhythmacanthidae, but it does not correspond to any genus described. Spiracanthus bovichthys is different in the number and spiralled distribution of its hooks in the proboscis. In the short proboscis, 3 groups of hooks are distinguished according to size, summing up to 150-190 hooks. The group of largest hooks are found in the apical part of the proboscis, and there are 10 diagonal rows of small hooks from the prebasal to basal proboscis. Its trunk is covered partially by small spines. Amphipod and isopods were the prey items shared among the host fish species and are the best candidates to be the intermediate hosts of S. bovichthys.     

The importance of foundation species identity: A field experiment with lichens and their associated micro-arthropod communities

Foundation species provide habitat and modify the availability of resources to other species. In nature, multiple foundation species may occur in mixture, but little is known on how their interactions shape the community assembly of associated species. Lichens provide both structural habitat and resources to a variety of associated organisms and thereby serve as foundation species. In this study, we use mat-forming lichens and their associated micro-arthropods as a miniature ecosystem to study potential synergies between foundation species diversity and the abundance and functional diversity of higher trophic levels. We created lichen patches with monocultures and mixtures of up to four species, and extracted Collembola (identified to species level), Oribatida, Mesostigmata, Pseudoscorpiones, and Araneae with Tullgren apparatuses after 106 days of incubation within a natural lichen mat. We found that different lichen species supported different arthropod abundances. For 19 out of a total of 55 lichen mixtures and arthropod groups, we found non-additive, synergistic effects on arthropod abundance, although the specific lichen mixture causing synergistic effects differed with arthropod group. In addition, synergistic effects on arthropod abundance were more common for arthropod groups at lower trophic levels. The functional diversity of lichen mixtures explained patterns in Collembola abundance, but in the opposite direction than hypothesized because synergistic responses were more frequent in functionally similar lichen mixtures. Finally, we found few effects of lichen mixture identity or diversity on the functional diversity of Collembola communities. When applied to large-scale ecosystems, our results suggest that understanding interactions between coexisting foundation species and identifying those species that drive synergistic effects of foundation species on consumer biota, is likely to be of importance to biodiversity conservation and restoration efforts.     

Further studies of the structure of human placental acid alpha-glucosidase

Acid alpha-glucosidase has been purified from human placenta to a specific activity of approximately 6800, (4-methylumbelliferyl-alpha-D-glucoside as a substrate) or 55,400 mumol g-1 min-1 (glycogen or maltose as substrate). The purified enzyme gives rise to multiple protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), i.e., a major doublet of 82K and 69K , a minor doublet of 25K and 21K , and a faint band of 100K. All of the molecular weight species stained as glycoproteins with an intensity apparently proportional to their protein content, and were present in enzyme from individuals homozygous for the allozyme alpha-Glu 1. Isoelectric focusing revealed only enzymatically active proteins which, when analysed by SDS-PAGE, gave rise to multiple molecular weight species. Chromatography of I125-labeled, purified enzyme on Bio-Gel P-100 revealed only a radiolabeled, high-molecular-weight species which corresponded with enzyme activity. These findings suggest that, in the native state, the mature enzyme exists as a high-molecular-weight species, which is dissociable in SDS to several low-molecular-weight species. These results are consistent with reports that a 100K primary product of translation is post-translationally modified to yield polypeptides of lower molecular weights, and that all of the molecular species are absent in cells genetically deficient for acid alpha-glucosidase. The possibility that the low-molecular-weight (20- 25K ) protein bands in SDS-gels corresponded to a previously reported low-molecular-weight species generated by treatment with guanidine-HCl was investigated. The I125-labeled, purified acid maltase was dissociated by guanidine into two equal peaks of approximately 64K and 28K molecular weight. Surprisingly, both peaks, when analyzed on SDS-gels, yielded identical and equally intensely staining bands of 64K molecular weight. These results suggest that the mature acid alpha-glucosidase is made up of polypeptides which are bonded in the native state by at least two different types of interaction, one type which is dissociable in SDS and one type which is dissociable in guanidine but not in SDS. The nature and possible function of the 25K polypeptide generated only by guanidine-HCl remains to be determined.     

The crowding effect in an artificially mixed population of three species

Three species of root vegetables and leaf vegetables were grown in mixed stands at various densities and mixing ratios in tow experiments. The reciprocal equation of the crowding effect for two-species mixtures was utilized for the three-species mixtures. Interactions between species in two- and three-species mixtures were compared using a density conversion factor which converts the density of one species to the density of the other species on the basis of its effect on the growth of the species. The mean plant weights in a three-species mixture could be estimated by putting the density conversion factors obtained from two-species mixtures into the reciprocal equations for a three-species mixture.     

Microencapsulation of human growth hormone within biodegradable polyester microspheres: protein aggregation stability and incomplete release mechanism.

Recombinant human growth hormone (rhGH) was encapsulated within poly(D,L-lactic-co-glycolic acid) microspheres by a double emulsion solvent evaporation method. A mixture of methylene chloride and ethyl acetate in varying volume ratios was used for the microsphere preparation. Protein release profiles from three different microsphere formulations demonstrated initial burst effects ranging from 28.2% to 54.7% after a 1-day incubation and exhibited no further significant releases up to 19 days. This was because the encapsulated rhGH with the microspheres was largely aggregated in a noncovalent fashion during the formulation. Nonaggregated water soluble rhGH species within the microspheres are likely to be responsible for the rapid release upon incubation. The initially released rhGH in the incubation medium, however, was composed of mostly monomer species with a small amount of dimer as probed by size-exclusion chromatography. Circular dichroism spectra of the initially released rhGH in the medium revealed that the conformation of the released rhGH was correctly folded relative to that of native rhGH, with little variation in alpha-helix contents depending on the formulations. The "nonrelease" mechanism after the initial burst release was attributed to nonspontaneously dissociable noncovalent protein aggregation and surface adsorption of rhGH present within the microspheres.     

AN ELECTROPHORETIC STUDY OF MIXTURES OF OVALBUMIN AND YEAST NUCLEIC ACID

Electrophoretic patterns of mixtures of ovalbumin and yeast nucleic acid indicate that the constituents migrate independently of each other in buffer solutions of 0.1 ionic strength and at pH values somewhat higher than the isoelectric point of the protein. In the isoelectric region, however, the patterns from the two sides of the channel exhibit asymmetries that can be explained by assuming the existence in the mixture of appreciable concentrations of a reversibly dissociable complex between the components. Formation of this complex is favored by increasing concentrations of the components and decreasing ionic strength. At pH values below the isoelectric point partial precipitation of the complex occurs. The patterns obtained from each side of the channel in the electrophoresis of a mixture of two components, which form a dissociable complex, indicate only two boundaries, aside from the δ and ε effects. One of these is a normal boundary whose displacement is proportional to the mobility of a component that has separated from the mixture. In the other boundary, however, dissociation of the complex occurs and consequently the displacement of this boundary corresponds to the mobility of neither component nor to that of the complex. Moreover, the areas under the refractive index gradient curves are not proportional to the stoichiometric concentrations of the components. However, equations are developed with the aid of which an electrophoretic analysis of the mixture is possible. This analysis requires the use of data from the patterns of both channels.     

Functional identity versus species richness: herbivory resistance in plant communities

The resistance of a plant community against herbivore attack may depend on plant species richness, with monocultures often much more severely affected than mixtures of plant species. Here, we used a plant–herbivore system to study the effects of selective herbivory on consumption resistance and recovery after herbivory in 81 experimental grassland plots. Communities were established from seed in 2002 and contained 1, 2, 4, 8, 16 or 60 plant species of 1, 2, 3 or 4 functional groups. In 2004, pairs of enclosure cages (1 m tall, 0.5 m diameter) were set up on all 81 plots. One randomly selected cage of each pair was stocked with 10 male and 10 female nymphs of the meadow grasshopper, Chorthippus parallelus. The grasshoppers fed for 2 months, and the vegetation was monitored over 1 year. Consumption resistance and recovery of vegetation were calculated as proportional changes in vegetation biomass. Overall, grasshopper herbivory averaged 6.8%. Herbivory resistance and recovery were influenced by plant functional group identity, but independent of plant species richness and number of functional groups. However, herbivory induced shifts in vegetation composition that depended on plant species richness. Grasshopper herbivory led to increases in herb cover at the expense of grasses. Herb cover increased more strongly in species-rich mixtures. We conclude that selective herbivory changes the functional composition of plant communities and that compositional changes due to selective herbivory depend on plant species richness.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : III. THE BASE EXCHANGE PROPERTIES OF COLLODION

1. Theoretical considerations lead to the conclusion that dissociable acidic groups present to a varying extent in different collodion preparations determine the electrochemical behavior of membranes cast from these preparations. It is further reasoned that the base exchange capacity of the collodion surfaces is the true quantitative measure of the abundance of the dissociable groups. 2. The concept of base exchange capacity and the base exchange method are discussed. The conditions which allow a purposeful application of the latter are stated. 3. The base exchange properties of a number of fibrous collodion preparations of different origins and after various types of treatment, having widely varying electrochemical activities, are determined. 4. With the chemical (titration) and physical (electrometric) methods employed, no regular correlation can be found between electrochemical activity and base exchange. The base exchange capacity which is necessary to cause even great electrochemical activity of collodion is extremely small. 5. Measurable to high base exchange capacity always seems to be associated with good or high electrochemical activity; but base exchange capacity too low to be definitely measurable with the available methods may be found with collodion preparations of high as well as with preparations of low electrochemical activity. 6. The bearing of these results upon the problem of the spatial and electrical structure of the collodion membrane is indicated briefly.     

The significance of regression line slope changes in the quantitative titration of complement components

The hypothesis is discussed that dissociable complexes are formed between elements of a test complement (C') and the reagent used to titrate it for a particular component. Calculations are presented which demonstrate that such complex formation may give considerable changes in slopes of percentage hemolysis-log dose regression lines obtained with mixtures of C' and reagent. It is shown that marked change of slope may occur with relatively little change in the value of the 50 per cent intercept.     

Quantifying species composition in root mixtures using two methods: near-infrared reflectance spectroscopy and plant wax markers

Understanding of plant interactions is greatly limited by our ability to identify and quantify roots belonging to different species. We proposed and compared two methods for estimating the root biomass proportion of each species in artificial mixtures: near-infrared reflectance spectroscopy (NIRS) and plant wax markers. Two sets of artificial root mixtures composed of two or three herbaceous species were prepared. The proportion of root material of each species in mixtures was estimated from NIRS spectral data (i) and the concentration patterns of n-alkanes (ii), n-alcohols (iii), and n-alkanes +n-alcohols combined (iv). For each data set, calibration equations were developed using multivariate statistical models. The botanical composition of root mixtures was predicted well for all the species considered. The accuracy varied slightly among methods: alkanes < alcohols = alkanes + alcohols < NIRS. Correlation coefficients between predicted and actual root proportions ranged from 0.89 to 0.99 for alkanes + alcohols predictions and from 0.97 to 0.99 for NIRS predictions. These two methods provide promising potential for understanding allocation patterns and competitive interactions.     

Latitudinal cline in segment number in an arthropod species, Strigamia maritima

Arthropods vary more than 30-fold in segment number. The evolutionary origins of differences in segment number among species must ultimately lie in intraspecific variation. Yet paradoxically, in most groups of arthropods, the number of segments is fixed for each species and shows no intra- or interpopulation variation at all. Geophilomorph centipedes are an exception to this general rule, and exhibit intraspecific variation in segment number, with differences between individuals being determined during embryonic development and hence independent of population age structure. Significant differences in segment number between different geographical populations of the same species have been previously reported, but insufficient sampling has been conducted to reveal any particular geographical pattern. Here, we reveal a latitudinal cline in segment number in the geophilomorph species Strigamia maritima: segment number in British populations decreases with distance north. This is the first such cline to be reported for any centipede species; indeed as far as we are aware it is the first such cline reported for any arthropod species. In vertebrates, fish are known to exhibit a latitudinal cline in segment number, but interestingly, this is in the opposite direction; fish add segments with increasing latitude, centipedes subtract them.