Regional environmental simulation of African cattle herding societies

Regional analyses of the interaction between human populations and natural resources must integrate landscape scale environmental problems. An approach that considers human culture, environmental processes, and resource needs offers an appropriate methodology. With this methodology, we analyze problems of food availability in African cattle-keeping societies. The analysis interrelates cattle biomass, forage availability, milk and blood production, crop yields, gathering, food subsidies, population, and variable precipitation. While an excess of cattle leads to overgrazing, cattle also serve as valuable food storage mechanisms during low rainfall periods. Food subsidies support higher population levels but do not alter drought-induced population fluctuations. Variable precipitation patterns require solutions that stabilize year-to-year food production and also address problems of overpopulation.     

Acetylcholinesterase molecular forms in the fast or slow muscles of the chicken and the pigeon

Molecular forms of acetylcholinesterase (AChE) were examined in various skeletal muscles of the chicken and the pigeon. In chicken pectoralis m., AChE was found to be restricted to endplate containing segments, and no asymmetric form could be detected in aneural samples. In the chicken muscles studied, a relation has been established between globular (G1,G2,G4) forms or asymmetric (A8,A12) forms, and muscle fibre types. Asymmetric forms are preponderant in fast-twitch muscles, whereas in slow tonic muscles 80% of the AChE activity is due to globular forms. However, comparison with pigeon muscles shows that AChE chicken muscle patterns may not be generalized.     

Simulation of marked root hair curling in Rhizobium-legume symbiosis

The soil bacterium Rhizobium infects its leguminous host plants in temperate regions of the world mostly by way of the growing root hairs. Root hair curling is a prerequisite for root hair infection, although sidelong root hair infections occasionally have been observed. The processes underlying Rhizobium -induced root hair curling are unknown.
Computer simulation of root hair growth indicates that one-sided tip growth inhibition by Rhizobium can result in root hair curling when three conditions are simultaneously fulfilled: 1) rhizobial growth inhibition is strong enough to prevent removal out of the tip growth range: 2) root hair surface growth between the attached Rhizobium and the root hair top is inhibited; 3) rhizobial growth inhibition is limited to one side of the root hair.
The results predict that root hair curling by stimulation of tip growth is improbable. This study accentuates the need for information about the growth processes contributing to tip growth in leguminous root hairs.     

Ion-specific diffusion rates through transmembrane protein channels. A molecular dynamics study

The migration of different alkali metal cations through a transmembrane model channel is simulated by means of the molecular dynamics technique. The parameters of the model are chosen in close relation to the gramicidin A channel. Coulomb- and van der Waals-type potentials between the ions and flexible carbonyl groups of the pore-forming molecule are used to describe the ion channel interaction. The diffusion properties of the ions are obtained from three-dimensional trajectory calculations. The diffusion rates for the different ions Li+, Na+, K+ and Rb+ are affected not only by the mass of the particles but also very strongly by their size. The latter effect is more pronounced for rigid channels, i.e., for binding vibrational frequencies of the CO groups with v greater than 400 cm-1. In this range the selectivity sequence for the diffusion rates is the inverse of that expected from normal rate theory but agrees with that found in experiments for gramicidin A.     

The effect of whey protein hydrolyzates on the lactic acid fermentation

Summary The batch fermentation of whey permeate to lactic acid was improved markedly by the addition of enzymehydrolyzed whey protein. Acid concentrations greater than 90 g/l were achieved at a productivity of 4.3 g/l per h and a 98% substrate use. Cell mass concentration reached 6 g/l. The acid productivity achieved is somewhat higher than that typical for fermentation of whole whey. The process economics, based on in-house hydrolyzate preparation, look promising. Presented in this paper are the experimental results showing the effects of hydrolyzate concentration on acid and cell mass production.     

Use of restrained molecular dynamics in water to determine three-dimensional protein structure: prediction of the three-dimensional structure of Ecballium elaterium trypsin inhibitor II

Refinement of distance geometry (DG) structures of EETI-II (Heitz et al.: Biochemistry 28:2392-2398, 1989), a member of the squash family trypsin inhibitor, have been carried out by restrained molecular dynamics (RMD) in water. The resulting models show better side chain apolar/polar surface ratio and estimated solvation free energy than structures refined "in vacuo." The consistent lower values of residual NMR constraint violations, apolar/polar surface ratio, and solvation free energy for one of these refined structures allowed prediction of the 3D folding and disulfide connectivity of EETI-II. Except for the few first residues for which no NMR constraints were available, this computer model fully agreed with X-ray structures of CMTI-I (Bode et al.: FEBS Lett. 242:285-292, 1989) and EETI-II complexed with trypsin that appeared after the RMD simulation was completed. Restrained molecular dynamics in water is thus proved to be highly valuable for refinement of DG structures. Also, the successful use of apolar/polar surface ratio and of solvation free energy reinforce the analysis of Novotny et al. (Proteins 4:19-30, 1988) and shows that these criteria are useful indicators of correct versus misfolded models.     

The effects of truncating long-range forces on protein dynamics

This paper considers the effects of truncating long-range forces on protein dynamics. Six methods of truncation that we investigate as a function of cutoff criterion of the long-range potentials are (1) a shifted potential; (2) a switching function; (3) simple atom-atom truncation based on distance; (4) simple atom-atom truncation based on a list which is updated periodically (every 25 steps); (5) simple group-group truncation based on distance; and (6) simple group-group truncation based on a list which is updated periodically (every 25 steps). Based on 70 calculations of carboxymyoglobin we show that the method and distance of long range cutoff have a dramatic effect on overall protein behavior. Evaluation of the different methods is based on comparison of a simulation's rms fluctuation about the average coordinates, the rms deviation from the average coordinates of a no cutoff simulation and from the X-ray structure of the protein. The simulations in which long-range forces are truncated by a shifted potential shows large rms deviations for cutoff criteria less than 14 A, and reasonable deviations and fluctuations at this cutoff distance or larger. Simulations using a switching function are investigated by varying the range over which electrostatic interactions are switched off. Results using a short switching function that switches off the potential over a short range of distances are poor for all cutoff distances. A switching function over a 5-9 A range gives reasonable results for a distance-dependent dielectric, but not using a constant dielectric. Both the atom-atom and group-group truncation methods based on distance shows large rms deviation and fluctuation for short cutoff distances, while for cutoff distances of 11 A or greater, reasonable results are achieved. Although comparison of these to distance-based truncation methods show surprisingly larger rms deviations for the group-group truncation, contrary to simulation studies of aqueous ionic solutions. The results of atom-atom or group-group list-based simulations generally appear to be less stable than the distance-based simulations, and require more frequent velocity scaling or stronger coupling to a heat bath.     

Expression of the gap junction protein connexin43 in embryonic chick lens: Molecular cloning,ultrastructural localization,and post-translational phosphorylation

Summary Lens epithelial cells are physiologically coupled to each other and to the lens fibers by an extensive network of intercellular gap junctions. In the rat, the epithelial-epithelial junctions appear to contain connexin43, a member of the connexin family of gap junction proteins. Limitations on the use of rodent lenses for the study of gap junction formation and regulation led us to examine the expression of connexin43 in embryonic chick lenses. We report here that chick connexin43 is remarkably similar to its rat counterpart in primary amino acid sequence and in several key structural features as deduced by molecular cDNA cloning. The cross-reactivity of an anti-rat connexin43 serum with chick connexin43 permitted definitive immunocytochemical localization of chick connexin43 to lens epithelial gap junctional plaques and examination of the biosynthesis of connexin43 by metabolic radiolabeling and immunoprecipitation. We show that chick lens cells synthesize connexin43 as a single, 42-kD species that is efficiently posttranslationally converted to a 45-kD form. Metabolic labeling of connexin43 with³²P-orthophosphate combined with dephosphorylation experiments reveals that this shift in apparent molecular weight is due solely to phosphorylation. These results indicate that embryonic chick lens is an appropriate system for the study of connexin43 biosynthesis and demonstrate for the first time that connexin43 is a phosphoprotein.     

Rates of synonymous substitution in plant nuclear genes

Summary The rate of synonymous nucleotide substitution in nuclear genes of higher plants has been estimated. The rate varies among genes by a factor of up to two, in a manner that is not immediately explicable in terms of base composition or codon usage bias. The average rate, in both monocots and dicots, is about four times higher than that in chloroplast genes. This leads to an estimated absolute silent substitution rate of 6 × 10^–9 substitutions per site per year that falls within the range of average rates (2–8 × 10^–9) seen in different mammalian nuclear genomes.