Comparative labor market performance of visaed and non-visaed migrants: Pacific islanders in Sydney

Using survey data for Tongan and Samoan migrants in Sydney the effects of visa restrictions on labor market performance of migrants are assessed. Univariate analysis suggests a positive association between unemployment and the unrestricted entry of Samoan step-migrants from New Zealand. A probit model of the determinants of unemployment is estimated with controls for human capital and demographic variables. While human capital endowments are important, visa restrictions do not have a significant effect on either group's employability. Implications for policy are discussed highlighting the complementarities between host country immigration policies and foreign aid programs.

Nitric oxide inhibition of the rat olfactory cyclic nucleotide-gated cation channel

The effects of nitric oxide (NO) and other cysteine modifying agents were examined on cyclic nucleotide-gated (CNG) cation channels from rat olfactory receptor neurons. The NO compounds, S-nitroso-cysteine (SNC) and 3-morpholino-sydnonomine (SIN-1), did not activate the channels when applied for up to 10 min. The cysteine alkylating agent, N-ethylmaleimide (NEM), and the oxidising agent, dithionitrobensoate (DTNB), were also without agonist efficacy. Neither SNC nor DTNB altered the cAMP sensitivity of the channels. However, 2-min applications of SIN-1, SNC and DTNB inhibited the cAMP-gated current to approximately 50% of the control current level. This inhibition showed no spontaneous reversal for 5 min but was completely reversed by a 2-min exposure to DTT. The presence of cAMP protected the channels against NO-induced inhibition. These results indicate that inhibition is caused by S-nitrosylation of neighboring sulfhydryl groups leading to sulfhydryl bond formation. This reaction is favored in the closed channel state. Since recombinantly expressed rat olfactory alpha and beta CNG channel homomers and alpha/beta heteromers are activated and not inhibited by cysteine modification, the results of this study imply the existence of a novel subunit or tightly bound factor which dominates the effect of cysteine modification in the native channels. As CNG channels provide a pathway for calcum influx, the results may also have important implications for the physiological role of NO in mammalian olfactory receptor neurons.

Phosphorylation of the C-terminal sites of human p53 reduces non-sequence-specific DNA binding as modeled with synthetic peptides

Phosphorylation of the tumor suppressor p53 is generally thought to modify the properties of the protein in four of its five independent domains. We used synthetic peptides to directly study the effects of phosphorylation on the non-sequence-specific DNA binding and conformation of the C-terminal, basic domain. The peptides corresponded to amino acids 361-393 and were either nonphosphorylated or phosphorylated at the protein kinase C (PKC) site, Ser378, or the casein kinase II (CKII) site, Ser392, or bis-phosphorylated on both the PKC and the CKII sites. A fluorescence polarization analysis revealed that either the recombinant p53 protein or the synthetic peptides bound to two unrelated target DNA fragments. Phosphorylation of the peptide at the PKC or the CKII sites clearly decreased DNA binding, and addition of a second phosphate group almost completely abolished binding. Circular dichroism spectroscopy showed that the peptides assumed identical unordered structures in aqueous solutions. The unmodified peptide, unlike the Ser378 phosphorylated peptide, changed conformation in the presence of DNA. The inherent ability of the peptides to form an alpha-helix could be detected when circular dichroism and nuclear magnetic resonance spectra were: taken in trifluoroethanol-water mixtures. A single or double phosphorylation destabilized the helix around the phosphorylated Ser378 residue but stabilized the helix downstream in the sequence.

Evolution of three-dimensional folds for a non-Newtonian plate in a viscous medium

We derive analytical solutions for the three-dimensional time-dependent buckling of a non-Newtonian viscous plate in a less viscous medium. For the plate we assume a power-law rheology. The principal, axes of the stretching D-ij in the homogeneously deformed ground state are parallel and orthogonal to the bounding surfaces of the plate in the flat state. In the model formulation the action of the less viscous medium is replaced by equivalent reaction forces. The reaction forces are assumed to be parallel to the normal vector of the deformed plate surfaces. As a consequence, the buckling process is driven by the differences between the in-plane stresses and out of plane stress, and not by the in-plane stresses alone as assumed in previous models. The governing differential equation is essentially an orthotropic plate equation for rate dependent material, under biaxial pre-stress, supported by a viscous medium. The differential problem is solved by means of Fourier transformation and largest growth coefficients and corresponding wavenumbers are evaluated. We discuss in detail fold evolutions for isotropic in-plane stretching (D-11 = D-22), uniaxial plane straining (D-22 = 0) and in-plane flattening (D-11 = -2D(22)). Three-dimensional plots illustrate the stages of fold evolution for random initial perturbations or initial embryonic folds with axes non-parallel to the maximum compression axis. For all situations, one dominant set of folds develops normal to D-11, although the dominant wavelength differs from the Biot dominant wavelength except when the plate has a purely Newtonian viscosity. However, in the direction parallel to D-22, there exist infinitely many modes in the vicinity of the dominant wavelength which grow only marginally slower than the one corresponding to the dominant wavelength. This means that, except for very special initial conditions, the appearance of a three-dimensional fold will always be governed by at least two wavelengths. The wavelength in the direction parallel to D-11 is the dominant wavelength, and the wavelength(s) in the direction parallel to D-22 is determined essentially by the statistics of the initial state. A comparable sensitivity to the initial geometry does not exist in the classic two-dimensional folding models. In conformity with tradition we have applied Kirchhoff's hypothesis to constrain the cross-sectional rotations of the plate. We investigate the validity of this hypothesis within the framework of Reissner's plate theory. We also include a discussion of the effects of adding elasticity into the constitutive relations and show that there exist critical ratios of the relaxation times of the plate and the embedding medium for which two dominant wavelengths develop, one at ca. 2.5 of the classical Biot dominant wavelength and the other at ca. 0.45 of this wavelength. We propose that herein lies the origin of parasitic folds well known in natural examples.

The solution structure of a copper(II) compound of a new cyclic octapeptide by EPR spectroscopy and force field calculations

A new cyclic octapeptide, cyclo(Ile-Ser-(Gly)Thz-Ile-Thr-(Gly)Thz) (PatN), related to patellamide A, has been synthesized and reacted with copper(II) and base to form mono- and dinuclear complexes. The coordination environments around copper(TI) have been characterized by EPR spectroscopy. The solution structure of the thermodynamically most stable product, a purple dicopper(TI) compound, has been examined by simulating weakly dipole-dipole coupled EPR spectra based upon structural parameters obtained from force field (MM and MD) calculations. The MM-EPR method produces a saddle-shaped structure for [Cu-2(PatN)(OH2)(6)] that is similar to the known solution structure of patellamide A and the known solid-state structure of [Cu-2(AscidH(2))CO3(OH2)(2)]. Compared with the latter, [Cu-2(PatN)] has no carbonate bridge and a significantly flatter topology. The MM-EPR approach to solution-structure determination for paramagnetic metallopeptides may find wide applications to other metallopeptides and metalloproteins.

Nuapapuin A and sigmosceptrellins D and E: New norterpene cyclic peroxides from a southern Australian marine sponge, Sigmosceptrella sp.

A Sigmosceptrella sp. from the Great Australian Eight, Australia, has yielded the new norditerpene cyclic peroxide, nuapapuin A (2a), and the norsesterterpene cyclic peroxide sigmosceptrellin D (3a), characterized as the corresponding methyl esters 2b and 3b. The crude methylated sponge extract also yielded the new norsesterterpene cyclic peroxide sigmosceptrellin E methyl ester (4). Relative stereochemistry about C2, C3, and C6 was assigned by established empirical rules and absolute stereochemistry by the advanced Mosher procedure. A plausible biosynthetic pathway has been proposed that rationalizes key transformations in the biosynthesis of all known norterpene cyclic peroxides and related norterpene ketones, dienes and sigmosceptrins.

Interaction of zinc(II) with the cyclic octapeptides, cyclo[Ile(Oxn)-D-Val(Thz)](2) and ascidiacyclamide, a cyclic peptide from Lissoclinum patella

The interactions between zinc salts and the naturally occurring cyclic octapeptide ascidiacyclamide in methanol, as well as a synthetic analogue cyclo[Ile(Oxn)-D-Val(Thz)](2), were monitored by H-1 NMR and CD spectroscopy. Three zinc complexes were identified, their relative amounts depending on the nature of the anion (perchlorate, triflate or chloride) and the presence or absence of base. Binding constants for two of the zinc species were calculated from CD or H-1 NMR spectra, [Zn(L - H)](+) (KZn(L-H) = [Zn(L - H)(+)]/[Zn2+][(L - H)(-)] = 10(7 +/- 2) M-1; 95% methanol/5% water, 298.0 K, NEt3/HClO4 buffer 0.04 M) and [ZnLCl](+) (K-ZnCIL = [ZnCIL+]/[Zn2+][Cl-][L] = 10(7.2) (+/-) (0.1) M-2; d(3)-methanol, 301 K).

Low-molecular-weight peptidic and cyclic antagonists of the receptor for the complement factor C5a

Activation of the human complement system of plasma proteins during immunological host defense can result in overproduction of potent proinflammatory peptides such as the anaphylatoxin C5a. Excessive levels of C5a are associated with numerous immunoinflammatory diseases, but there is as yet no clinically available antagonist to regulate the effects of C5a. We now describe a series of small molecules derived from the C-terminus of C5a, some of which are the most potent low-molecular-weight C5a receptor antagonists reported to date for the human polymorphonuclear leukocyte (PMN) C5a receptor. H-1 NMR spectroscopy was used to determine solution structures for two cyclic antagonists and to indicate that antagonism is related to a turn conformation, which can be stabilized in cyclic molecules that are preorganized for receptor binding. While several cyclic derivatives were of similar antagonistic potency, the most potent antagonist was a hexapeptide-derived macrocycle AcF[OPdChaWR] with an IC50 = 20 nM against a maximal concentration of C5a (100 nM) on intact human PMNs. Such potent C5a antagonists may be useful probes to investigate the role of C5a in host defenses and to develop therapeutic agents for the treatment of many currently intractable inflammatory conditions.

T cell-mediated and non-specific inflammatory mechanisms contribute to the skin pathology of HPV 16 E6E7 transgenic mice

One of three lines of mice transgenic for the E6 and E7 genes of human papillomavirus type 16 (HPV16) expressed from an alpha A-crystallin promoter also expresses the transgene ectopically in the skin. This line, designated alpha ACE6E7#19, develops skin disease from 3 months of age, characterised by epidermal hyperplasia and eventual skin loss. Administration of complete Freund's adjuvant (CFA) to alpha ACE6E7#19 mice, but not to nontransgenic littermate controls, induced local epidermal hyperplasia which was histologically similar to the spontaneously arising skin pathology. Local application of 2,4-dinitrochlorobenzene (DNCB) to DNCB-sensitised aACE6E7#19 mice, but not DNCB-sensitised controls, also induced hyperplasia. Treatment with cyclosporin A (CsA) or systemic depletion of CD4+ cells significantly reduced the incidence of skin disease. These data suggest that local inflammation, and cytokines produced by T helper cells, contribute to the induction of hyperplastic skin disease in alpha ACE6E7#19 mice. Spontaneous skin disease with similar histological appearance, frequency, age of onset and severity in alpha ACE6E7#19 mice was observed in scid-/- aACE6E7#19 mice, despite immune paresis. Antigen-specific immune responses and T-cell cytokines a re therefore not necessary for the induction of skin disease. We propose that epidermal hyperplasia associated with HPV16 E6 and E7 expression in skin is accelerated by local secretion of pro-inflammatory cytokines, whose production can be enhanced by activated CD4+ T cells.

Rectification of the olfactory cyclic nucleotide-gated channel by intracellular polyamines

Polyamine-induced inward rectification of cyclic nucleotide-gated channels was studied in inside-out patches from rat olfactory neurons. The polyamines, spermine, spermidine and putrescine, induced an 'instantaneous' voltage-dependent inhibition with K-d values at 0 mV of 39, 121 mu M and 2.7 mM, respectively. Hill coefficients for inhibition were significantly < 1, suggesting an allosteric inhibitory mechanism. The Woodhull model for voltage-dependent block predicted that all 3 polyamines bound to a site 1/3 of the electrical distance through the membrane from the internal side. Instantaneous inhibition was relieved at positive potentials, implying significant polyamine permeation. Spermine also induced exponential current relaxations to a 'steady-state' impermeant level. This inhibition was also mediated by a binding site 1/3 of the electrical distance through the pore, but with a K-d of 2.6 mM. Spermine inhibition was explained by postulating two spermine binding sites at a similar depth. Occupation of the first site occurs rapidly and with high affinity, but once a spermine molecule has bound, it inhibits spermine occupation of the second binding site via electrostatic repulsion. This repulsion is overcome at higher membrane potentials, but results in a lower apparent binding affinity for the second spermine molecule. The on-rate constant for the second spermine binding saturated at a low rate (similar to 200 sec(-1) at +120 mV), providing further evidence for an allosteric mechanism. Polyamine-induced inward rectification was significant at physiological concentrations.

Chemical synthesis and folding pathways of large cyclic polypeptide: Studies of the cystine knot polypeptide kalata B1

Kalata B1 is a member of a new family of polypeptides, isolated from. plants, which have a cystine knot structure embedded within an amide-cyclized backbone. This family of molecules are the largest known cyclic peptides, and thus, the mechanism of synthesis and folding is of great interest. To provide information about both these phenomena, we have synthesized kalata B1 using two distinct strategies. In the first, oxidation of the cysteine residues of a linear precursor peptide to form the correct disulfide bonds results in folding of the three-dimensional structure and preorganization of the termini in close proximity for subsequent cyclization. The second approach involved cyclization prior to oxidation. In the first method, the correctly folded peptide was produced only in the presence of partially hydrophobic solvent conditions. These conditions are presumably required to stabilize the surface-exposed hydrophobic residues. However,; in the synthesis,involving cyclization prior to oxidation, the cyclic reduced peptide folded to a significant degree in the absence of hydrophobic solvents and even more efficiently in the presence of hydrophobic solvents. Cyclization clearly has a major effect on the folding pathway and facilitates formation of the correctly disulfide-bonded form in aqueous solution; In addition to facilitating folding to a compact stable structure cyclization has an important effect on biological activity as assessed by hemolytic activity.

Gene transfer and expression of a non-viral polycation-based vector in CD4(+) cells

CD4-selective targeting of an antibody-polycation-DNA complex was investigated The complex was synthesized with the anti-CD4 monoclonal antibody B-F5, polylysine(268) (pLL) and either the pGL3 control vector containing the luciferase reporter gene or the pGeneGrip vector containing the green fluorescent protein (GFP) gene. B-F5-pLL-DNA complexes inhibited the binding of I-125-B-F5 to CD4(+) Jurkat cells, while complexes synthesised either without B-F5 or using a non-specific mouse IgG1 antibody had little or no effect Expression of the luciferase reporter gene was achieved in Jurkat cells using the B-F5-pLL-pGL3 complex and was enhanced in the presence of PMA. Negligible luciferase activity was defected with the non-specific antibody complex in Jurkat cells or with the B-F5-pLL-pGL3 complex in the CD4(-) K-562 cells. Using complexes synthesised with the pGeneGrip vector, the transfection efficiency in Jurkat and K-562 cells was examined using confocal microscopy. More than 95% of Jurkat cells expressed GFP and the level of this expression was markedly enhanced by PMA. Negligible GFP expression was seen in K-562 cells or when B-F5 was replaced by a nonspecific antibody. Using flow cytometry, fluorescein-labelled complex showed specific targeting to CD4(+) cells in a mixed cell population from human peripheral blood. These studies demonstrate the selective transfection of CD4(+) T-lymphoid cells using a polycation-based gene delivery system. The complex may provide a means of delivering anti-HIV gene therapies to CD4(+) cells in vivo.

Novel vascular graft grown within recipient's own peritoneal cavity

A method by which to overcome the clinical symptoms of atherosclerosis is the insertion of a graft to bypass an artery blocked or impeded by plaque. However, there may be insufficient autologous mammary artery for multiple or repeat bypass, saphenous vein may have varicose degenerative alterations that can lead to aneurysm in high-pressure sites, and small-caliber synthetic grafts are prone to thrombus induction and occlusion. Therefore, the aim of the present study was to develop an artificial blood conduit of any required length and diameter from the cells of the host for autologous transplantation. Silastic tubing, of variable length and diameter, was inserted into the peritoneal cavity of rats or rabbits. By 2 weeks, it had become covered by several layers of myofibroblasts, collagen matrix, and a single layer of mesothelium. The Silastic tubing was removed from the harvested implants, and the tube of living tissue was everted such that it now resembled a blood vessel with an inner lining of nonthrombotic mesothelial cells (the intima), with a media of smooth muscle-like cells (myofibroblasts), collagen, and elastin, and with an outer collagenous adventitia. The tube of tissue (10 to 20 mm long) was successfully grafted by end-to-end anastomoses into the severed carotid artery or abdominal aorta of the same animal in which they were grown. The transplant remained patent for at least 4 months and developed structures resembling elastic lamellae. The myofibroblasts gained a higher volume fraction of myofilaments and became responsive to contractile agonists, similar to the vessel into which they had been grafted. It is suggested that these nonthrombogenic tubes of living tissue, grown in the peritoneal cavity of the host, may be developed as autologous coronary artery bypass grafts or as arteriovenous access fistulae for hemodialysis patients.