Dust accumulation in the canopy: a potential cause of dental microwear in primates.

Dental microwear researchers consider exogenous grit or dust to be an important cause of microscopic wear on primate teeth. No study to date has examined the accumulation of such abrasives on foods eaten by primates in the forest. This investigation introduces a method to collect dust at various heights in the canopy.

A method for characterizing transition concertedness from polymer dynamics computer simulations.

A statistical method based on classifying the transitions among a set of dihedral angles within an "energy transfer window" is developed, and used to analyze Brownian (BD) and molecular dynamics (MD) simulations of the acyl chains in a lipid bilayer, and MD of neat hexadecane. It is shown for the BD simulation that when a transition of the dihedral angle in the center of the chain occurs, a transition of a particular next nearest neighbor (or angle 2-apart) will follow concertedly with a probability of approximately 0.10 within a time window of approximately 3 ps.

Unliganded c-erbA/thyroid hormone receptor induces trkB expression in neuroblastoma cells.

Neurotrophins are responsible for the differentiation and survival of neurons in the developing and in the adult nervous system. They bind to specific membrane receptors with tyrosine kinase activity whose prototype is the product of the trkA proto-oncogene. TrkB, a member of this family, is the receptor for the neurotrophins brain derived growth factor (BDNF) and neurotrophins-3, -4/5.

Molecular dynamics simulations of a lipid bilayer and of hexadecane: an investigation of membrane fluidity.

Molecular dynamics simulations of a fluid-phase dipalmitoyl phosphatidylcholine lipid bilayer in water and of neat hexadecane are reported and compared with nuclear magnetic resonance spin-lattice relaxation and quasi-elastic neutron scattering data. On the 100-picosecond time scale of the present simulations, there is effectively no difference in the reorientational dynamics of the carbons in the membrane interior and in pure hexadecane. Given that the calculated fast reorientational correlation times and the "microscopic" lateral diffusion of the lipids show excellent agreement with the experimental results, it is concluded that the apparently high viscosity of the membrane is more closely related to molecular interactions on the surface rather than in the interior.

Conformational states of a TT mismatch from molecular dynamics simulation of duplex d (CGCGATTCGCG).

The TT mismatch region in duplex d (CGCGATTCGCG) was studied using a 500-ps molecular dynamics (MD) simulation in water, and a series of 1-ps MD simulations and energy minimizations in vacuum. The DNA maintained its duplex structure, although the mismatch region showed significantly higher flexibility than the GC regions. The predominant conformation in the 500-ps MD simulation involved an average -42 degrees propeller twist between T6 and T'6, and a -22 degree buckle between A5 and T'7.

Backbone dynamics of calmodulin studied by 15N relaxation using inverse detected two-dimensional NMR spectroscopy: the central helix is flexible.

The backbone dynamics of Ca(2+)-saturated recombinant Drosophila calmodulin has been studied by 15N longitudinal and transverse relaxation experiments, combined with 15N(1H) NOE measurements. Results indicate a high degree of mobility near the middle of the central helix of calmodulin, from residue K77 through S81, with order parameters (S2) in the 0.5-0.

Langevin dynamics of peptides: the frictional dependence of isomerization rates of N-acetylalanyl-N'-methylamide.

The rate constant for the transition between the equatorial and axial conformations of N-acetylalanyl-N'-methylamide has been determined from Langevin dynamics (LD) simulations with no explicit solvent. The isomerization rate is maximum at collision frequency gamma = 2 ps-1, shows diffusive character for gamma greater than or equal to 10 ps-1, but does not approach zero even at gamma = 0.01 ps-1.

Mean field stochastic boundary molecular dynamics simulation of a phospholipid in a membrane.

Computer simulations of phospholipid membranes have been carried out by using a combined approach of molecular and stochastic dynamics and a mean field based on the Marcelja model. First, the single-chain mean field simulations of Pastor et al. [(1988) J.

Model for the structure of the lipid bilayer.

A detailed model for the structure and dynamics of the interior of the lipid bilayer in the liquid crystal phase is presented. The model includes two classes of motion: (i) the internal dynamics of the chains, determined from Brownian dynamics simulations with a continuous version of the Marcelja mean-field potential, and (ii) noncollective reorientation (axial rotation and wobble) of the entire molecule, introduced by a cone model. The basic unit of the model is a single lipid chain with field parameters adjusted to fit the 2H order parameters and the frequency-dependent 13C NMR T1 relaxation times of dipalmitoyl phosphatidylcholine bilayers.

T3 receptor occupancy and T3 levels in plasma and cytosol during rat brain development.

The concentration and occupancy of the thyroid hormone receptor have been measured in rat brain nuclear extracts at the end of the fetal period and during the postnatal period. Receptor occupancy attained maximal values at postnatal day 15 (52% of total receptor binding sites occupied by T3) and correlated with plasma and cytosol total and free T3. The values for these parameters showed greater differences throughout development than did receptor occupancy.

Theoretically determined three-dimensional structures for amphipathic segments of the HIV-1 gp41 envelope protein.

Three-dimensional computer models for two segments of the C terminus of gp41, the transmembrane AIDS envelope protein, which may form amphipathic alpha-helices, have been generated using structure prediction techniques combined with energy minimization and molecular dynamics simulations. Regions gp41(772-790) and gp41(828-848) of the HXB2 strain of HIV-1 display extraordinarily high hydrophobic moment maxima as alpha-helices and when in an antiparallel conformation exhibit charge complementarity, implying that they may bind with each other and associate with the membrane. The feasibility of this hypothesis was tested in a series of computer simulations of these peptides, extended by several residues to include additional charge pairing.

Migration and development: implications and recommendations for policy.

"The conventional wisdom on the relationship between migration and development in the Caribbean Basin can be summarized in two propositions: that migration from the region to the United States is an 'escape valve,' benefitting the sending countries; and that development reduces the pressures for migration. This article examines both propositions and concludes they are misleading or inaccurate. Emigration costs the sending countries in serious ways and often impedes development.

Activity-induced patterns of dental abrasion in prehistoric Pakistan: evidence from Mehrgarh and Harappa.

A detailed investigation of worn teeth should reveal a record of past activity patterns including information regarding diet, food preparation methods, and craft or occupational activities. Anthropological studies of the extensive dental samples from Neolithic (MR 3) and Chalcolithic (MR 2) levels at Mehrgarh, Baluchistan, and Bronze Age Harappa, Punjab, yielded several interesting examples of unusual dental abrasion. This paper provides macro- and microscopic (scanning electron microscope) descriptions of three types of activity-induced dental abrasion: 1) interproximal tooth grooving and interproximal abrasion patches, 2) facial abrasion of maxillary anterior teeth, and 3) lingual abrasion of maxillary incisors in association with rounded wear of lower incisors.

Effects of maternal iodine deficiency on thyroid hormone economy of lactating dams and pups: maintenance of normal cerebral 3,5,3'-triiodo-L-thyronine concentrations in pups during major phases of brain development.

Female rats were fed a diet with a low iodine content (LID), or the same LID supplemented with KI, and mated. Fetuses were obtained at 17 and 21 days of gestation, or pups were killed at different ages after birth. The dams on LID were markedly iodine deficient and developed a large goiter.

Theoretically determined three-dimensional structure for the repeating tetrapeptide unit of the circumsporozoite coat protein of the malaria parasite Plasmodium falciparum.

A model for the three-dimensional structure of the repeating Asn-Pro-Asn-Ala tetrapeptide of the immunodominant circumsporozoite protein of Plasmodium falciparum has been developed. A trial structure in the form of a type I beta turn with asparagine side chains hydrogen-bonded to the backbone peptide linkages was used as a starting point. A repeating oligomer of this trial structure was modeled using energy minimization and molecular dynamics computer simulations in conjunction with image boundary conditions.

A recognition site on synthetic helical oligonucleotides for monoclonal anti-native DNA autoantibody.

The binding site in native DNA for a murine monoclonal anti-DNA autoantibody was investigated by measurements of competitive binding of a series of synthetic helical oligonucleotides. The antibody bound to a (dG-dC)3 or (dG-dC)4 core in the center of a base-paired octadecanucleotide. Reactions of analogues containing modifications or substitutions at specific sites indicated that the antibody bound to portions of cytosine and guanine in the major groove, a limited region of the backbone, and the 2-amino group of one guanine in the minor groove.

Effects of maternal iodine deficiency on the L-thyroxine and 3,5,3'-triiodo-L-thyronine contents of rat embryonic tissues before and after onset of fetal thyroid function.

Female rats were placed on a low iodine diet (LID) or LID supplemented with KI. They were mated 3-6 months later. Maternal and embryonic tissues were obtained both before the onset of fetal thyroid function, at 11 and 17 days of pregnancy, and at 21 days of gestation.

Effects of maternal hypothyroidism on the weight and thyroid hormone content of rat embryonic tissues, before and after onset of fetal thyroid function.

Embryonic tissues were obtained from normal (C) and thyroidectomized (T) rats between 9 and 21 days of pregnancy. We determined the number and weight, as well as the T4 and T3 contents (RIA), of 9- to 12-day-old embryotrophoblasts, of 13- to 21-day-old embryos and placentas, and of liver, lung, and brain from 20- and 21-day-old fetuses. T4 and T3 were found in all samples obtained from C dams, both before and after onset of fetal thyroid function.