Formation, derivatization and applications of bacterial cellulose

Acetobacter xylinum produces highly crystalline cellulose extracellularly using glucose as a carbon source. The polymer formed is free of other biogenic compounds, separable in a simple way and characterized by its high water-absorption capacity. Stepwise solvent exchange from water to unpolar solvents leads to a drastic decrease of the water content of the bacterial cellulose without decrease of the highly swollen and activated state. Heterogeneous as well as homogeneous derivatizations, e.g. carboxymethylation, silylation and acetylation, were performed on the wet or dried biopolymer. Furthermore, different methods for formation of hollow fibres during biosynthesis were investigated. Such tubes may have applications as biocompatible material in medicine.

Insulin inhibits dephosphorylation of adenosine 3',5'-monophosphate response element-binding protein/activating transcription factor-1: effect on nuclear phosphoserine phosphatase-2a

We examined the effects of insulin on the phosphorylation state of cAMP response element-binding protein (CREB) in normal rat adipocytes. Insulin increased in vivo phosphorylation of CREB by 40%. Although both phosphoprotein phosphatase-1 and -2A dephosphorylate CREB and activating transcription factor-1, insulin action appears to be mediated via its strong inhibitory effect on nuclear phosphatase-2A (PP-2A) activity. Using in vitro protein kinase-A-phosphorylated activating transcription factor-1 as a substrate, we found that insulin inhibited nuclear PP-2A activity by 80% (P < 0.001), which represents approximately 50% of the total nuclear phosphatase activity. Greater than 50% of the effect of insulin was observed at 0.3 nM and 2 min of exposure. These findings are the first indicator that a signal initiated by a cell surface tyrosine kinase receptor may regulate nuclear PP-2A activity and thereby affect the phosphorylation state of transcription factors.