Properties of TiO2-polyacrylic acid dispersions with potential for molecular recognition.

Titanium dioxide (TiO2)/polyacrylic acid (PAA) (TiO2/PAA) particles were formed by mixing PAA and an acidic solution of TiO2 nanoparticles in dimethylformamide (DMF) followed by heat treatment. TEM and particle analysis showed that the resulting particles had a narrow size distribution. The colloid was very stable and aggregation was not observed over a wide pH range (3-9) or at high salt concentration. The residual carboxylic acid of PAA could be modified via EDC/NHS activation to form an amide bond with a protein. An antibody was attached to the hybrid nanoparticle and specific binding to antigen was monitored by surface plasmon resonance. The results suggest that TiO2/PAA nanoparticles are candidates as the base component of a photocatalytic system with potential for substrate selectivity.

Stable expression of a heterogeneous gene introduced via gene targeting into the HPRT locus of human fibrosarcoma cells.

To obtain a cell line that maintains stability of gene expression is important for industrial production of therapeutic proteins from recombinant cells. In this study, we attempted to improve the stability of expression of an exogenous gene by using the gene-targeting method in cultured cells. In our gene-targeting system, the green fluorescent protein (GFP) gene was used as an exogenous reporter gene targeted to the locus of the endogenous hypoxanthine phosphoribosyl transferase (HPRT) gene, which is constitutively expressed. Cell lines selected using markers of the targeting DNA were cultivated for 129 days without any drug selection, and the expression levels of GFP protein and the chromosomal structure of the gfp gene in these cell lines were evaluated. Cell lines in which gfp genes were randomly integrated into the genome showed decreased GFP expression, which resulted from loss of genes or attenuation of transcription. In contrast, cell lines in which the gfp gene was targeted to the hprt locus maintained a stable chromosomal structure and stable expression of the gfp gene, even after prolonged cultivation. These results suggest that constitutively expressed endogenous gene loci may be suitable positions for stable expression of exogenous genes, and that the gene-targeting strategy presented here may be useful for generation of cell lines for industrial protein production.

Fructose-2,6-bisphosphate contents were increased in response to salt, water and osmotic stress in leaves of Bruguiera gymnorrhiza by differential changes in the activity of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase.

The steady-state level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase (F6P2K/F26BPase) transcript has been found to be raised in the mangrove Bruguiera gymnorrhiza treated with 500 mM NaCl for 6 h. In the present study, we assayed both F6P2K/F26BPase activity and fructose-2,6-bisphosphate (F26BP) contents in leaves of salt- and water-stressed B. gymnorrhiza. In the plants treated with 500 mM NaCl, no increase in transcript level was observed after 1 day of treatment, while both the ratio between F6P2K and F26BPase activity (K/P ratio) and leaf F26BP level were about two-fold higher than in control plants. Several water stress-associated treatments, including 500 mM NaCl treatment for 6 h, 1 M mannitol treatment for 6 h and dehydration treatment, resulted in increases in leaf F26BP level as compared with water-grown plants. The raised levels of F26BP in osmotically stressed plants treated with NaCl and mannitol were accompanied with increased transcript levels and subsequent increases in both F6P2K and F26BPase activities, while the increase in F26BP levels in dehydrated plants was attributed to an increase in K/P ratio without an increase in transcript levels. These results suggest that, although both treatments resulted in increases in F26BP levels, B. gymnorrhiza differentially responds to osmotic stress and water stress.