Towards bioinspired superhydrophobic poly(L-lactic acid) surfaces using phase inversion-based methods

The water repellency and self-cleaning ability of many biological surfaces has inspired many fundamental and practical studies related to the development of synthetic superhydrophobic surfaces. However, the investigation of such substrates made of biodegradable polymers has been scarce. Simple approaches based on a single step, performed at room temperature (and pressure), were implemented to obtain superhydrophobic poly(L-lactic acid) (PLLA) surfaces via phase inversion-based methods, without addition of low-surface-energy compounds. Water contact angles above 150 degrees were obtained using some processing conditions. In such cases scanning electronic microscopy micrographs of such surfaces revealed a clear rough texture composed by leafy clusters with micro-nano binary structures. Such materials could be used in specific environmental and biomedical applications, namely in implantable materials or in antibacterial or antithrombogenic surfaces.     

Testing mechanisms of DNA sliding by architectural DNA-binding proteins: dynamics of single wild-type and mutant protein molecules in vitro and in vivo

Architectural DNA-binding proteins (ADBPs) are abundant constituents of eukaryotic or bacterial chromosomes that bind DNA promiscuously and function in diverse DNA reactions. They generate large conformational changes in DNA upon binding yet can slide along DNA when searching for functional binding sites. Here we investigate the mechanism by which ADBPs diffuse on DNA by single-molecule analyses of mutant proteins rationally chosen to distinguish between rotation-coupled diffusion and DNA surface sliding after transient unbinding from the groove(s). The properties of yeast Nhp6A mutant proteins, combined with molecular dynamics simulations, suggest Nhp6A switches between two binding modes: a static state, in which the HMGB domain is bound within the minor groove with the DNA highly bent, and a mobile state, where the protein is traveling along the DNA surface by means of its flexible N-terminal basic arm. The behaviors of Fis mutants, a bacterial nucleoid-associated helix-turn-helix dimer, are best explained by mobile proteins unbinding from the major groove and diffusing along the DNA surface. Nhp6A, Fis, and bacterial HU are all near exclusively associated with the chromosome, as packaged within the bacterial nucleoid, and can be modeled by three diffusion modes where HU exhibits the fastest and Fis the slowest diffusion.     

Synthesis of first trimester placental alkaline phosphatase in cultured human term placental cells

Alkaline phosphatase activity in human placental cells transformed by a tsA mutant of simian virus 40 (SV40) can be greatly induced by growing these cells at 40 degrees C, the temperature at which the tsA transformants regain their nontransformed phenotype. The induction of alkaline phosphatase in these cells requires the synthesis of both RNA and protein. The induced alkaline phosphatase from a SV40 tsA30 mutant-transformed term placental cell line (TPA30-1) was purified, characterized, and compared with alkaline phosphatase from term placenta and first trimester placenta. The form of alkaline phosphatase found in TPA30-1 cells differs from the phosphatase of term placenta in physiochemical and immunological properties. The TPA30-1 phosphatase is, however, indistinguishable from the alkaline phosphatase of human first trimester placenta by several criteria, including electrophoretic mobility, apparent molecular weight (Mr = 165,000), size of monomeric subunit (Mr = 77,000), heat lability, and sensitivity to inhibition by amino acids and EDTA. In addition, alkaline phosphatase from both TPA30-1 cells and first trimester placenta can be inactivated by antiserum to liver alkaline phosphatase but not by antiserum to term placental alkaline phosphatase. The induction of first trimester phosphatase in cells derived from term placenta provides a system for the study of alkaline phosphatase gene regulation in human placenta.     

Increased Levels of Monodehydroascorbate Radical in UV-B-Irradiated Broad Bean Leaves

Light-induced monodehydroascorbate (MDA) radical productionwas not detectable by EPR spectroscopy in untreated broad beanleaves, but it was observed after exposing the leaves to UV-B(280–320 nm) irradiation. After this pre-treatment, alow level of MDA radicals was also detectable without illumination.Light-induced MDA, MDA production in the dark, oxygen evolution,quantum yield of PSII as measured by Chi fluorescence, MDA producingand reducing enzyme activities were determined and comparedin leaves after irradiation with various doses of UV-B. Ourresults suggest that UV-B irradiation disturbs the balance ofMDA radical production and reduction, resulting in increasedlight induced MDA signal. The enhancement of ascorbate photooxidationat the UV-B damaged donor side of PSII appears as a major factorin this process. (Received November 22, 1996; Accepted March 25, 1997)     

Ascorbate in thylakoid lumen as an endogenous electron donor to Photosystem II: Protection of thylakoids from photoinhibition and regeneration of ascorbate in stroma by dehydroascorbate reductase

Photoinhibition of the electron transport activity from tyrosine Z (Y_Z) in PS II to NADP⁺in Tris-treated thylakoids was suppressed by electron donation with either diphenylcarbazide or ascorbate (AsA) during the photoinhibition treatment. This suggests that AsA prevents donor side-induced photoinhibition in vivo as an endogenous donor. AsA in the lumen is photooxidized to monodehydroascorbate (MDA) in Tris-treated thylakoids, as detected by electron spin resonance spectrometry, but not in oxygenic thylakoids. Redox analysis of pyridine nucleotide in the presence of either MDA reductase or dehydroascorbate (DHA) reductase showed that the MDA photoproduced in the lumen is disproportionated to AsA and DHA, and the DHA leaking into the stroma is reduced to AsA by DHA reductase. No leakage of MDA through the thylakoid membrane was observed. Thus, the DHA-reducing enzyme system is indispensable in maintaining AsA concentrations in chloroplasts.