Some physical and chemical properties of trypsin-digested nucleoprotein

A DNA-peptide complex that is soluble in 0.2m-sodium chloride can be prepared by trypsin digestion of calf thymus nucleoprotein. The trypsin-digested nucleoprotein molecule contains about 70% of DNA and 30% of peptides by weight, and consists of one DNA molecule associated with arginine-rich peptides. A series of trypsin-digested nucleoprotein preparations differing only in molecular weight were prepared by blending. The intrinsic viscosity and average sedimentation coefficient were determined for each of these preparations. Then the DNA was isolated from each preparation and the hydrodynamic measurements were repeated on the DNA. From a comparison of these results it was concluded that the presence of the complex-forming peptides causes a large decrease in intrinsic viscosity of the DNA and an increase in sedimentation coefficient. In addition, the hydrodynamic data indicate that the DNA-peptide complex behaves like a coil in solution but is more compact than the same length of DNA. The ;melting' profiles, streptomycin precipitation curves and maximum viscosities obtained with ethidium bromide binding for the trypsin-digested nucleoprotein are similar to those of purified DNA, and markedly different from those of undigested nucleoprotein. These findings suggest that the peptides are not strongly associated with the DNA, and that secondary valency forces are involved in the binding.     

Some physical properties of paramyosin from earthworms

Paramyosin was prepared from earthworms (Lumbricus terrestris) by two different methods that have been used in the past. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate shows that the older method yields slightly degraded material (mostly β- and γ-paramyosin) while the newer method yields essentially intact, i.e., α-, paramyosin. Physical studies, particularly circular dichroism, light scattering, and sedimentation velocity show that the native molecule is a double α-helical coiled coil of molecular weight 200,000, length 1200 Å, and diameter 20 Å. These properties are the same as reported previously for molluscan paramyosin. Also like clam paramyosin, the worm protein molecule loses its helix content and dissociates into its two constituent polypeptide chains upon exposure to sufficient concentration of Gdn-HCl. Furthermore, the same partially denatured states can be reached from either native or completely denatured proteins, indicating that they are all equilibrium states. However, the Gdn · HCl-induced denaturation profile for the worm paramyosin is quite different from the clam. The helix content of worm paramyosin diminishes monophasically with increasing concentration of Gdn-HCl, showing that the molecule does not possess a region of special stability such as its clam analog boasts. This conclusion is supported by experiments on papain digestion of worm paramyosin, wherein no resistent core is seen.     

Some water-related physical properties of maize root-cap mucilage

Abstract The dry weight (0.1%) and water potential -7 kPa) of root-cap mucilage from 3-d-old axenically grown maize seedlings have been determined. The results suggest strong gelling properties and weak water-holding capacity for the mucilage. Root tips from seedlings grown under low or high water stress were fixed by freeze-substitution. Micrographs showed that in both conditions, mucilage was secreted into the periplasmic space and extruded through the cell wall, though in dry conditions, the mucilage was tightly pressed against the root-cap surface. Histochemical and structural evidence is presented indicating chemical changes in the composition of the mucilage upon extrusion and a sharp increase in its hydration at increasing distance from the secretory cells. The possible functions of the root-cap mucilage in the rhizosphere are examined in light of these findings.     

Some physical properties of coat material fromBacillus stearothermophilus spores

Coat material fromBacillus stearothermophilus spores has been examined for the following properties: X-ray diffraction pattern, infrared absorption spectrum, mechanical strength, and melting temperatures of the crystalline regions. The X-ray diffraction pattern of the coat material is different from that of both α-and β-keratin. The high melting temperature of the crystalline material indicates that its bonding is more stable than that of α- or β-keratin. The mechanical strength of the coat material ?10⁹N/m² is shown to be high enough to allow the coat to support the internal pressure in bacterial spores. This pressure has been postulated to produce a partial dehydration, which increases the ability of bacterial spores to withstand high temperatures in water.     

Photo-cross-linked PLA-PEO-PLA hydrogels from self-assembled physical networks: mechanical properties and influence of assumed constitutive relationships

Poly(lactide)-block-poly(ethylene oxide)-block-poly(lactide) (PLA-PEO-PLA) triblock copolymers are known to form physical hydrogels in water as a result of the polymer's amphiphilicity. Their mechanical properties, biocompatibility, and biodegradability have made them attractive for use as soft tissue scaffolds. However, the network junction points are not covalently cross-linked, and in a highly aqueous environment these hydrogels adsorb more water, transform from gel to sol, and lose the designed mechanical properties. In this article, a hydrogel was formed by the use of a novel two-step approach. In the first step, the end-functionalized PLA-PEO-PLA triblock was self-assembled into a physical hydrogel through hydrophobic micelle network junctions, and in the second step, this self-assembled physical network structure was locked into place by photo-cross-linking the terminal acrylate groups. In contrast with physical hydrogels, the photo-cross-linked gels remained intact in phosphate-buffered solution at body temperature. The swelling, degradation, and mechanical properties were characterized, and they demonstrated an extended degradation time (approximately 65 days), an exponential decrease in modulus with degradation time, and a tunable shear modulus (1.6-133 kPa). We also discuss the various constitutive relationships (Hookean, neo-Hookean, and Mooney-Rivlin) that can be used to describe the stress-strain behavior of these hydrogels. The chosen model and assumptions used for data fitting influenced the obtained modulus values by as much as a factor of 3.5, which demonstrates the importance of clearly stating one's data fitting parameters so that accurate comparisons can be made within the literature.     

Some physical and immunological properties of ox kidney biliverdin reductase.

The liver, kidney and spleen of the mouse and rat and the kidney and spleen of the ox express a monomeric form of biliverdin reductase (Mr 34,000), which in the case of the ox kidney enzyme exists in two forms (pI 5.4 and 5.2) that are probably charge isomers. The livers of the mouse and rats express, in addition, a protein (Mr 46,000) that cross-reacts with antibodies raised against the ox kidney enzyme and may be related to form 2 described by Frydman, Tomaro, Awruch & Frydman [(1983) Biochim. Biophys. Acta 759, 257-263]. Higher-Mr forms appear to exist in the guinea pig and hamster. The ox kidney enzyme has three thiol groups, of which two are accessible to 5,5'-dithiobis-(2-nitrobenzoate) in the native enzyme. Immunocytochemical analysis reveals that biliverdin reductase is localized in proximal tubules of the inner cortex of the rat kidney. Biliverdin reductase antiserum also stains proximal tubules in human and ox kidney. The staining of podocytes in glomeruli of ox kidney with antiserum to aldose reductase is particularly prominent. The localization of biliverdin reductase in the inner cortical zone of rat kidney is similar to that described for glutathione S-transferase YfYf, and it is suggested that one function of this 'intracellular binding protein' may be to maintain a low free concentration of biliverdin to allow biliverdin reductase to operate efficiently.