127-I]- or carrier-free [125-I]monoiodoinsulin.

Insulin was enzymatically moniodinated with 127-I or 125-I, and an improved method of purification by anion exchange chromatography was employed. (127-I)Monoiodoinsulin was identified by spectrophotometric analysis and its molar extinction coefficient determined to be 6.31 times 10-3 M-1 cm minus 1. The observed specific activity of carrier-free (125-I)monoidoinsulin was close to the theoretical value (378mCi/mg). The monoiodotyrosyl residue of monoidoinsulin was shown to be solvent-exposed. The ionic properties of the substituted hormone were altered at pH values close to the pK of monoiodotyrosine (8.85), but the pI was unchanged (5.65). (127-I)Monoiodoinsulin formed rhombohedral crystals and co-crystallized with native insulin. Monoidoinsulin was indistinguishable from insulin with respect to binding to two out of three guinea pig anti-insulin sera, to binding to IM9 cultured human lymphocytes, and to binding to isolated rat hepatocyte plasma membranes. The potency of monoidoinsulin was not statistically different from that of insulin in the rat fat cell bioassay and in the mouse convulsion assay. An insulin-degrading enzyme extracted from rat liver degraded monoiodoinsulin less readily than native insulin; monoiodoinsulin was a competitive inhibitor of insulin degradation, and the Km values were 30 nM AND 78 NM for monoidoinsulin and native insulin, respectively. It is concluded that monoidination does not markedly alter the three-dimensional structure of the molecule and that only a few sensitive biological systems are able to distinguish the monoidinated from the native hormone.     

Salt effects on bacteriophage T7-I

The thermal denaturation as a measure of the structural stability of the nucleoprotein in bacteriophage T7 has been studied in dependence of the ionic environment. Optical density and circular dichroism melting curves measured at wavelengths characterizing either the DNA or protein conformational changes were compared to identify different steps of the denaturation and to follow the effect of the ions. Monovalent salts strengthen the helical structure of intraphage DNA logarithmically in the way as they do in the case of isolated double-stranded DNA. Mg2+ and Ca2+ at very low concentrations stabilize the DNA helicity. Higher divalent ion concentrations decrease the stability of the double helix because of the repulsive ionic interactions. The high structural sensitivity of DNA in the presence of Mg2+ and Ca2+ in this "in situ" environment can be related to the biological role of these ions.     

Myxomycetes from Orissa-(India)-I

Summary Seven species of Myxomycetes belonging to 6 genera,Ceratiomyxa fruticulosa (Mull.)Macbr.,Hemitrichia serpula (Scop.)Rost.,Diachea splendens Peck.,Stemonitis Smithii Macbr.,Stemonitis fusca Roth.,Comatricha typhoides (Bull.)Rost. andDiderma hemisphericum (Bull.)Hornem. have been figured and described, of whichStemonitis Smithii Macbr. is a new record in India.     

Osmotic regulation in juvenile oncorhynchus kisutch (Walbaum)-I

Summary Experiments related to the salinity tolerance of coho salmon fry 44 to 65 days old, were realized. They suggested a tolerance to 18 p.p.th. (or less) salinity, for the youngest fish. These however became more and more tolerant as they grew older. When 59 days old, young coho survived in 22 p.p.th. salt water. The 50% lethal level was then 26 p.p.th.Another experiment tested the possibility of acclimatizing 59-day old fry to salinity. Coho fry acclimatized for nine days to 21 p.p.th. salt water, survived for the next seven days in 28 p.p.th. salt water.A last experiment showed that the direct transfer of 59-day old coho from 24 p.p.th. (or less) salt water to fresh water could be entirely successful.

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Résumé Des alevins de saumon argenté, agés de 44à 55 jours, furent testés pour leur tolérance à différentes concentrations salines. Les plus jeunes poissons se montrèrent résistants à des salinités de 18 p.p.mille au maximum. Cette tolérance cependant s'accrût avec l'age. Agés de 59 jours ils survécurent à 22 p.p.mille, le niveau léthal pour la moitié de la population étant alors de 26 p.p.mille.La possibilité d'acclimater des alevins agés de 59 jours à de fortes concentrations salines fut aussi investiguée. De tels saumons, acclimatés pendant neuf jours à une salinité de 21 p.p.mille, survécurent sept jours dans de l'eau de mer peu diluée (28 p.p.mille).Le transfert soudain d'alevins agés de 59 jours d'une solution saline (24 p.p.mille) à de l'eau fraîche s'opéra sans mortalité.

     

End-to-end self-assembly of RADA 16-I nanofibrils in aqueous solutions

RADARADARADARADA (RADA 16-I) is a synthetic amphiphilic peptide designed to self-assemble in a controlled way into fibrils and higher ordered structures depending on pH. In this work, we use various techniques to investigate the state of the peptide dispersed in water under dilute conditions at different pH and in the presence of trifluoroacetic acid or hydrochloric acid. We have identified stable RADA 16-I fibrils at pH 2.0–4.5, which have a length of ～200–400 nm and diameter of 10 nm. The fibrils have the characteristic antiparallel β-sheet structure of amyloid fibrils, as measured by circular dichroism and Fourier transform infrared spectrometry. During incubation at pH 2.0–4.5, the fibrils elongate very slowly via an end-to-end fibril-fibril aggregation mechanism, without changing their diameter, and the kinetics of such aggregation depends on pH and anion type. At pH 2.0, we also observed a substantial amount of monomers in the system, which do not participate in the fibril elongation and degrade to fragments. The fibril-fibril elongation kinetics has been simulated using the Smoluchowski kinetic model, population balance equations, and the simulation results are in good agreement with the experimental data. It is also found that the aggregation process is not limited by diffusion but rather is an activated process with energy barrier in the order of 20 kcal/mol.     

Solid state self-assembly mechanism of RADA16-I designer peptide

We report that synthetic RADA16-I peptide transforms to β-strand secondary structure and develops intermolecular organization into β-sheets when stored in the solid state at room temperature. Secondary structural changes were probed using solid state nuclear magnetic resonance spectroscopy (ssNMR) and Fourier transform infrared spectroscopy (FTIR). Intermolecular organization was analyzed via wide-angle X-ray diffraction (WAXD). Observed changes in molecular structure and organization occurred on the time scale of weeks during sample storage at room temperature. We observed structural changes on faster time scales by heating samples above room temperature or by addition of water. Analysis of hydration effects indicates that water can enhance the ability of the peptide to convert to β-strand secondary structure and assemble into β-sheets. However, temperature dependent FTIR and time dependent WAXD data indicate that bound water may hinder the assembly of β-strands into β-sheets. We suggest that secondary structural transformation and intermolecular organization together produce a water-insoluble state. These results reveal insights into the role of water in self-assembly of polypeptides with hydrophilic side chains, and have implications on future optimization of RADA16-I nanofiber production.     

Crystal structure analysis of NP24-I: a thaumatin-like protein

The crystal structure of NP24-I, an isoform of the thaumatin-like protein (TLP) NP24 from tomato, has been reported. A prominent acidic cleft is observed between domains I and II of the three-domain structure of this antifungal protein, a feature common to other antifungal TLPs. The defensive role of the TLPs has also been attributed to their beta-1,3-glucanase activity and here too the acidic cleft is reported to play a vital role. NP24 is known to bind beta-glucans and so a linear beta-1,3-glucan molecule has been docked in the interdomain cleft of NP24-I. From the docked complex it is observed that the beta-glucan chain is so positioned in the cleft that a Glu and Asp residue on either side of it may form a catalytic pair to cause the cleavage of a glycosidic bond. NP24 has been reported to be an allergenic protein and an allergenic motif could be identified on the surface of the helical domain II of NP24-I. In addition, some allergenic motifs bearing high similarity/identity with some predicted Ig-E binding motifs of closely related allergenic TLPs like Jun a 3 (Juniperus ashei, from mountain cedar pollen) and banana-TLP have been identified on the molecular surface of NP24-I.