The effects of polylysine (PLL) and PLL-asialoorosomucoid (AsOR) on DNA condensation have been analyzed by AFM. Different types of condensed DNA structures were observed, which show a sequence of conformational changes as circular plasmid DNA molecules condense progressively. The structures range from circular molecules with the length of the plasmid DNA to small toroids and short rods with approximately 1/6 to 1/8 the contour length of the uncondensed circular DNA. Single plasmid molecules of 6800 base pairs (bp) condense into single toroids of approximately 110 nm diameter, measured center-to-center. The results are consistent with a model for DNA condensation in which circular DNA molecules fold several times into progressively shorter rods. Structures intermediate between toroids and rods suggest that at least some toroids may form by the opening up of rods as proposed by Dunlap et al. [(1997) Nucleic Acids Res. 25, 3095]. Toroids and rods formed at lysine:nucleotide ratios of 5:1 and 6:1. This high lysine:nucleotide ratio is discussed in relation to entropic considerations and the overcharging of macroions. PLL-AsOR is much more effective than PLL alone for condensing DNA, because several PLL molecules are attached to a single AsOR molecule, resulting in an increased cation density.

The atomic force microscope (AFM) was used to assay the extent of DNA condensation in approximately 100 different complexes of DNA with polylysine (PL) or PL covalently attached to the glycoproteins asialoorosomucoid (AsOR) or orosomucoid (OR). The best condensation of DNA was obtained with 10 kDa PL covalently attached to AsOR, at a lysine:nucleotide (Lys:nt) ratio of 5:1 or higher. These conditions produce large numbers of toroids and short rods with contour lengths of 300-400 nm. Some DNA condensation into shortened thickened structures was seen with 10 kDa PL attached to AsOR at Lys:nt ratios of 1.6:1 and 3:1. Some DNA condensation was also seen with 4 kDa PL at Lys:nt ratios of 3:1 and higher. Little DNA condensation was seen with PL alone or with PL convalently attached to OR at Lys:nt ratios up to 6:1. AsOR-PL enhanced gene expression in the mouse liver approximately 10- to 50-fold as compared with PL alone.

Molecular assemblies containing phospholipids and conjugated polydiacetylene lipids exhibit unique biochromatic properties and have attracted increasing interest in recent years as potential bio-and chemosensors. We present a detailed study of the properties of mixed films formed at the air-water interface, which consist of phospholipid molecules and diacetylene lipids. The organization of the films has been characterized by surface pressure-area isotherms. Application of atomic force microscopy, polarized optical microscopy, and UV-vis spectroscopy provides further insight into the structures and interactions of the film components. The data indicate that the two constituents in the film are miscible at low surface pressure, while segregation of phospholipid and polymer domains occurs at higher surface pressures. The distribution and interactions between the diacetylene and phospholipid domains additionally depends on the molar fraction of phospholipid in the film. Characterization of the structural properties of the polydiacetylene domains in the films points to a formation of organized trilayer and multilayer phases at high surface pressures and high diacetylene concentrations.

The rheological properties of the sulfated polysaccharide of the red microalga Porphyridium sp., a heteropolymer with a molecular weight of 3-5 x 10(6) Da, indicated that this material might be an excellent candidate for lubrication applications: the viscosity of the polysaccharide is stable over a range of temperatures, pH values, and salinities. In this study, various rheological and lubricant properties of the polysaccharide were evaluated in comparison with those of a widely used biolubricant, hyaluronic acid. The viscosity of the Porphyridium sp. polysaccharide remained essentially unchanged in a temperature range of 25-70 degrees C. In tribology tests on a ball-on-flat ceramic pair, the values for the friction coefficient and wear rate for the pair lubricated with polysaccharide were remarkably lower than those for hyaluronic acid, especially at high loads. In a test on a steel ring/ultrahigh-molecular-weight polyethylene (UHMWPE) block pair, the wear tracks on the surface of the UHMWPE were more pronounced for hyaluronic acid than for the polysaccharide. Atomic force microscopy showed that the polysaccharide was effectively adsorbed onto mica surfaces, forming ultrathin coating layers in the nanometer range. As is required for biolubricant applications, the polysaccharide was not degraded by hyaluronidase. The stability of the Porphyridium sp. polysaccharide to heat and to hyaluronidase combined with its ability to reduce friction and wear indicate its potential as an advantageous biolubricant.