The concentration-dependence of macromolecular parameters.

Theories concerning the concentration-dependence of sedimentation and diffusion coefficients for macro-molecules in dilute solution are compared and discussed, together with their experimental basis. An attempt has been made to clarify an important uncertainty still present in the literature as to whether sedimentation coefficients should be corrected for solvent or solution density. It is pointed out that the two processes yield the same extrapolation limit but different concentration-dependencies, which have, however, been related. A general expression is derived thermodynamically for the concentration-dependence of diffusion that includes the coefficient of the concentration term involved in sedimentation (on the basis of sedimentation coefficients corrected from solution density). For rigid spherical particles the expression is shown to be exactly equivalent to one given by Batchelor [(1976) J. Fluid Mech. 74, 1-29], which was derived on the basis of sedimentation coefficients corrected from solvent density. Finally, we discuss the concentration-dependence of apparent weight-average relative molecular masses ('molecular weights') (from, e.g., sedimentation equilibrium) and note an important omission in some earlier representations.     

Effect of ethanol on glutathione concentration in isolated hepatocytes.

1. Ethanol induces a decrease in GSH (reduced glutathione) concentration is isolated hepatocytes. Maximal effects appear at 20 mM-ethanol. The concentration-dependence of this decrease is paralleled by the concentration-dependence of the activity of alcohol dehydrogenase. 2. Pyrazole, a specific inhibitor of alcohol dehydrogenase, prevents the ethanol-induced GSH depletion. 3. Acetaldehyde, above 0.05 mM, also promotes a decrease in GSH concentration in hepatocytes. 4. Disulfiram (0.05 mM), an inhibitor of aldehyde dehydrogenase, potentiates the fall in GSH concentration caused by acetaldehyde. 5. The findings support the hypothesis that acetaldehyde is responsible for the depletion of GSH induced by ethanol. 6. Methionine prevents the effect of alcohol or acetaldehyde on GSH concentration in hepatocytes.     

Ion Uptake in Higher Plants and KCl Stimulation of Plasmalemma Adenosine Triphosphatase: Comparison of Models

Criteria for the acceptance or rejection of the dual, the cooperative, and the multiphasic model of ion uptake are given and are used to evaluate the models on the basis of previously published analyses. In addition, mathematical representations of the models are fitted to concentration-dependence data for various ions and plant tissues by a general curve fitting program. The calculated parameters are evaluated for biological relevance, and the fit is compared by statistical analysis. The kinetics of ion uptake in higher plants are found to be consistent with the concept of multiphasic uptake mechanisms, while the dual and the cooperative model must be rejected. KCl stimulation of plasmalemma-bound ATPases is also shown to obey multiphasic kinetics, thus strengthening the correlation between ion uptake and membrane-bound ATPases.     

Chromatographic evidence of the self-association of oxyhemoglobin in concentrated solutions: its biological implications.

Expressions that take into account the effects of thermodynamic non-ideality, described in terms of a high-order virial expansion, are derived for the concentration-dependence of the weight-average partition coefficient in exclusion chromatography of a single solute and of a solute undergoing reversible self-association. Comparison of the concentration-dependences predicted by those expressions with results obtained for bovine and human oxyhemoglobins on CPG-10-120 porous glass beads in 0.156 I phosphate-chloride buffer, pH 7.3, shows that neither oxyhemoglobin conforms with the concept of it being a single alpha 2 beta 2 entity with Stokes radius of 3.13 nm, the experimental value. Previously published osmotic pressure and sedimentation equilibrium results are also shown to be inconsistent with this concept. On the other hand, both sets of exclusion chromatography results are consistent with the joint operation of thermodynamic non-ideality and reversible association of the alpha 2 beta 2 species. From the magnitude of the equilibrium constant, derived for either of two possible modes of association, it is calculated that only half of the oxyhemoglobin would be in the alpha 2 beta 2 states under conditions of oxygen saturation and a concentration of 320 g/liter, that pertaining in the red blood cell. The consequences of this association phenomenon are discussed in relation to the oxygen binding curves obtained by others in the presence and absence of 2,3-diphosphoglycerate (DPG). An explanation is provided of the observed dependence on hemoglobin concentration of oxygen-binding in the presence of DPG, and of the absence of such an effect in DPG-free solutions. It is concluded that the control of oxygen binding to hemoglobin in the physiological situation involves the joint operation of self-association and allosteric effects.     

Testing Hypotheses in the Two-period Change-over with Binary Data

The paper proposes a general model for analysizing two-period change-over designs with binary data. The model includes tests for carry-over effects, treatment and period effects in analogy to the well-known ANOVA-model for continuous data. Minimum modified χ²-statistics are derived and formulas for desk calculators are given.     

The evolution of altruism: Correlation,cost, and benefit

A simple and general criterion is derived for the evolution of altruism when individuals interact in pairs. It is argued that the treatment of this problem in kin selection theory and in game theory are special cases of this general criterion.My thanks to James Crow, Carter Denniston, Lee Dugarkin, David Wilson, and an anonymous referee of this journal for helpful discussion.     

Preferential cleavage of amino- and carboxyl-terminal oligopeptides from vasoactive intestinal polypeptide by human recombinant enkephalinase (neutral endopeptidase, EC 3.4.24.11)

Human recombinant enkephalinase (neutral endopeptidase, EC 3.4.24.11) cleaved synthetic vasoactive intestinal peptide (VIP1-28) with time-and peptidase concentration-dependence, which left less than 30% intact after 30 micrograms was incubated at 37 degrees C with 0.1 micrograms and 10 micrograms of peptidase for 120 min and 15 min, respectively. The rank order of relative rates of peptidolysis amino-terminal to hydrophobic amino acids was Ala4 and Val5 greater than Tyr22 and Ile26 much greater than Leu13 and Met17. The many effects of VIP1-28 on epithelial cell and leukocyte functions thus may be influenced by degradation of the mediator by enkephalinase at the surface of target cells.     

High-affinity receptors for vasoactive intestinal peptide on human myeloma cells

Cultured human myeloma cells of the U266 line and leukemic T cells of the Jurkat line bound synthetic [125I]Tyr10-vasoactive intestinal peptide1-28 ([125I]VIP1-28) specifically and with an affinity similar to that of neuroendocrine cells. Specific binding reached equilibrium after 2 h at 22 degrees C for both myeloma cells and T cells, attained a maximum of 57 to 71% of total binding, and was reversed in 1.5 to 3 h by an excess of non-radioactive VIP1-28. Analyses of the ligand concentration-dependence of binding of the ligand concentration-dependence of binding of [125I]VIP1-28 revealed a mean Kd of 7.6 nM for a mean of 41,207 receptors per myeloma cell and 5.2 nM for 12,266 receptors per T cell. The relative affinity of binding of mast cell-derived VIP10-28 free acid and synthetic analogues suggested differences in specificity between lymphocyte and neuroendocrine receptors. Distinct sets of receptors thus appear to mediate the effects of VIP on functions of both antibody-producing cells and T cells.     

Thermodynamics, mechanical and electrical properties of biomembranes

A set of thermodynamic fundamental equations has been derived, including chemical potentials of immobile components of a biomembrane. The results obtained are compatible with those known in the theory of shells, but the approach developed is more general. The influence of an outer electric field on the isotropic tension of a biomembrane has been discussed. The thermodynamic relations derived are used for the treatment of intracellular pressure changes recently observed by Terakawa (1985, J. Physiol. 369, 229) in the squid giant axon at potential variations.     

QUANTITATIVE GENETIC MODELS FOR DEVELOPMENT,EPIGENETIC SELECTION,AND PHENOTYPIC EVOLUTION

Herein we describe a general multivariate quantitative genetic model that incorporates two potentially important developmental phenomena, maternal effects and epigenetic effects. Maternal and epigenetic effects are defined as partial regression coefficients and phenotypic variances are derived in terms of age-specific genetic and environmental variances. As a starting point, the traditional quantitative genetic model of additive gene effects and random environmental effects is cast in a developmental time framework. From this framework, we first extend a maternal effects model to include multiple developmental ages for the occurrence of maternal effects. An example of maternal effects occurring at multiple developmental ages is prenatal and postnatal maternal effects in mammals. Subsequently, a model of intrinsic and epigenetic effects in the absence of maternal effects is described. It is shown that genetic correlations can arise through epigenetic effects, and in the absence of other developmental effects, epigenetic effects are in general confounded with age-specific intrinsic genetic effects. Finally, the two effects are incorporated into the basic quantitative genetic model. For this more biologically realistic model combining maternal and epigenetic effects, it is shown that the phenotypic regressions of offspring on mother and offspring on father can be used in some cases to estimate simultaneously maternal effects and epigenetic effects.     

A mixture theory analysis for passive transport in osmotic loading of cells

The theory of mixtures is applied to the analysis of the passive response of cells to osmotic loading with neutrally charged solutes. The formulation, which is derived for multiple solute species, incorporates partition coefficients for the solutes in the cytoplasm relative to the external solution, and accounts for cell membrane tension. The mixture formulation provides an explicit dependence of the hydraulic conductivity of the cell membrane on the concentration of permeating solutes. The resulting equations are shown to reduce to the classical equations of Kedem and Katchalsky in the limit when the membrane tension is equal to zero and the solute partition coefficient in the cytoplasm is equal to unity. Numerical simulations demonstrate that the concentration-dependence of the hydraulic conductivity is not negligible; the volume response to osmotic loading is very sensitive to the partition coefficient of the solute in the cytoplasm, which controls the magnitude of cell volume recovery; and the volume response is sensitive to the magnitude of cell membrane tension. Deviations of the Boyle-van't Hoff response from a straight line under hypo-osmotic loading may be indicative of cell membrane tension.     

The effects of acetaldehyde on nitrogenase, hydrogenase and photosynthesis in the cyanobacterium Anabaena cylindrica.

Acetaldehyde was shown to be an irreversible inhibitor of nitrogenase, hydrogenase, CO2 fixation and growth in the cyanobacterium Anabaena cylindrica, but had no effect on photosynthetic electron flow as measured by Methyl Viologen-dependent O2 uptake. The concentration-dependence of the inhibition of nitrogenase and hydrogenase activities was determined, and it was shown that acetaldehyde inhibition poses problems for anaerobic experiments in which the activities of these enzymes are measured in the presence of the frequently used glucose/glucose oxidase/catalase/ethanol O2 trap. It is suggested that acetaldehyde may find use as an inhibitor in experiments designed to separate electron flow through the photosystems from consequent fixation of CO2 and N2.     

Initiation of somatic embryogenesis in white spruce (Picea glauca): genetic control,culture treatment effects,and implications for tree breeding

The degree of genetic control and the effects of cultural treatments on somatic embryogenesis (SE) in white spruce were investigated with material derived from six-parent diallel crosses, including reciprocals. Thirty zygotic embryos from both immature and mature cones of each family were cultured in media with either 2,4-D or Picloram immediately after the collection of cones and after 2 months of cold storage. There were significant differences in SE initiation between immature and mature explants, and fresh and cold-stored seeds, but there was no significant differences with culture media effect. Significant variances due to families and to family x treatment interactions were found. The mean percentage of explants that initiated SE in each family ranged from 3.3% to 54.6%, with an overall average of 30.5%. The partitioning of family variance revealed that 21.7% was due to general combining ability effects, 3.5% was due to maternal effects, and 5.5% was due to reciprocal effects, but that the specific combining ability (SCA) was negligible. Variance due to interactions of family x treatments collectively accounted for 32.6%, while the remaining 37.8% of variation was accounted for by random error. However, when comparing the responses obtained with the treatment combinations, the SE response for freshly excised immature embryo explants showed comparatively large SCA variance, whereas the SCA variance was very small in the other treatment combinations.     

Characteristics of a stable, filamentous mutant of a coccoid blue-green alga

Filamentous mutants were induced in a coccoid blue-green alga, Agmenellum quadruplicatum strain BG1, after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (NTG). The mutants fall into two general classes: filaments with cross walls and filaments without cross walls. All mutants of these general types derived from BG1 are stable and have growth rates the same as or very similar to the wild type under a variety of conditions. Detailed examination of one mutant, 53SB2, revealed no difference in deoxyribonucleic acid content nor in base ratios. Mutant 53SB2 did not revert to the normal cell size and shape when grown under different physical conditions nor upon the addition of potential reversing agents to the basal medium. It is our general experience that filamentous mutants such as those described here in BG1 are commonly induced in other coccoid blue-green algae after NTG treatment.     

The General Theory of Mapping Functions for Random Genetic Recombination

The general theory of mapping functions for random genetic recombination is derived without reference to physical models. The results are of particular relevance to asymmetric recombination (preferential recombination of the alleles of either parent) and include the effects of lethal lesions. It is noted that the assumption of randomness determines the mapping functions uniquely so that they are independent of the specifications of any stochastic physical model of recombination. In particular, the functions derived from physical models by Haldane, Wu, Wood and Verhoef and de Haan are special cases of those derived here. A general principle for the testing of genetic linkage is formulated which is valid for both symmetric and asymmetric recombination.     

Patterns of treatment effects in subsets of patients in clinical trials

We discuss the practice of examining patterns of treatment effects across overlapping patient subpopulations. In particular, we focus on the case in which patient subgroups are defined to contain patients having increasingly larger (or smaller) values of one particular covariate of interest, with the intent of exploring the possible interaction between treatment effect and that covariate. We formalize these subgroup approaches (STEPP: subpopulation treatment effect pattern plots) and implement them when treatment effect is defined as the difference in survival at a fixed time point between two treatment arms. The joint asymptotic distribution of the treatment effect estimates is derived, and used to construct simultaneous confidence bands around the estimates and to test the null hypothesis of no interaction. These methods are illustrated using data from a clinical trial conducted by the International Breast Cancer Study Group, which demonstrates the critical role of estrogen receptor content of the primary breast cancer for selecting appropriate adjuvant therapy. The considerations are also relevant for general subset analysis, since information from the same patients is typically used in the estimation of treatment effects within two or more subgroups of patients defined with respect to different covariates.     

Influence of macrophage products on the release of plasminogen activator, collagenase, beta-glucuronidase and prostaglandin E2 by articular chondrocytes.

We describe the effects of products of mononuclear phagocytes on the secretory activity of chondrocytes. The primary confluent cultures of rabbit articular chondrocytes were exposed to standard medium alone or enriched with conditioned medium obtained from cultures of rabbit peritoneal macrophages, the mouse macrophage cell line P388D1 or human blood mononuclear cells. Four markers of release were assessed, the neutral proteinases plasminogen activator and collagenase, the acid hydrolase beta-glucuronidase and prostaglandin E2, and the kinetics of their changes were monitored. Chondrocytes that were cultured in standard medium secreted large amounts of plasminogen activator, some beta-glucuronidase, but no collagenase, and released only minor amounts of prostaglandin E2. The addition of conditioned medium from rabbit macrophages induced a rapid release of large quantities of prostaglandin E2 and an abundant secretion of collagenase, while abolishing or strongly decreasing plasminogen activator secretion. In addition, beta-glucuronidase secretion was markedly enhanced. The decrease in secretion of plasminogen activator appeared to reflect a diminished production, since no evidence was found for the generation of inhibitors or for an accelerated extracellular breakdown of the enzyme. Conditioned media of the mouse and human mononuclear cells influenced the secretory activities of rabbit articular chondrocytes in a similar way, suggesting that the factor (or factors) acting on chondrocytes is produced by a variety of macrophages, and that its action is not species-restricted. The time course and concentration-dependence of the effects observed indicate that the secretion of plasminogen activator and collagenase are influenced in a strictly reciprocal fashion by the macrophage products. The release of prostaglandin E2 paralleled that of collagenase.     

Epistasis,inbreeding depression,and the evolution of self-fertilization

Inbreeding depression resulting from partially recessive deleterious alleles is thought to be the main genetic factor preventing self-fertilizing mutants from spreading in outcrossing hermaphroditic populations. However, deleterious alleles may also generate an advantage to selfers in terms of more efficient purging, while the effects of epistasis among those alleles on inbreeding depression and mating system evolution remain little explored. In this article, we use a general model of selection to disentangle the effects of different forms of epistasis (additive-by-additive, additive-by-dominance, and dominance-by-dominance) on inbreeding depression and on the strength of selection for selfing. Models with fixed epistasis across loci, and models of stabilizing selection acting on quantitative traits (generating distributions of epistasis) are considered as special cases. Besides its effects on inbreeding depression, epistasis may increase the purging advantage associated with selfing (when it is negative on average), while the variance in epistasis favors selfing through the generation of linkage disequilibria that increase mean fitness. Approximations for the strengths of these effects are derived, and compared with individual-based simulation results.     

Gibbs-Duhem-based relationships among derivatives expressing the concentration dependences of selected chemical potentials for a multicomponent system

For a two-component system, a derivative that specifies the concentration-dependence of one chemical potential can be calculated from the corresponding derivative of the other chemical potential by applying the Gibbs-Duhem Equation. To extend the practical utility of this binary thermodynamic linkage to systems having any number of components, we present a derivation based on a previously unrecognized recursive relationship. Thus, for each independently variable component, kappa, any derivative of its chemical potential, mukappa, with respect to one of the mole ratios {mkappa identical with nkappa/nomega} is related to as a characteristic series of progressively higher order derivatives of muomega for a single "probe" component, omega, with respect to certain of the {mkappa}. For aqueous solutions in which omega is solvent water and one or more of the solutes (kappa) is dilute, under typical conditions each sum of terms expressing a derivative of mukappa consists of at most a few numerically significant contributions, which can be quantified, or at least estimated, by analyzing osmometric data to determine how the single chemical potential muomega depends on the {mkappa} without neglecting any significant contributions from the other components. Expressions derived here also will provide explicit criteria for testing various approximations built into alternative analytic strategies for quantifying derivatives that specify the {mkappa} dependences of mukappa for selected components. Certain quotients of these derivatives are of particular interest in so far as they gauge important thermodynamic effects due to "preferential interactions".     

The frequency spectrum of a mutation,and its age,in a general diffusion model

General formulae are derived for the probability density and expected age of a mutation of frequency x in a population, and similarly for a mutation with b copies in a sample of n genes. A general formula is derived for the frequency spectrum of a mutation in a sample. Variable population size models are included. Results are derived in two frameworks: diffusion process models for the frequency of the mutation; and birth and death process models. The coalescent structure within the mutant gene group and the non-mutant group is considered.