High-affinity NGF binding requires coexpression of the trk proto-oncogene and the low-affinity NGF receptor.

Nerve growth factor (NGF) interacts with two different low-affinity receptors that can be distinguished by affinity crosslinking. Reconstitution experiments by membrane fusion and transient transfection into heterologous cells indicate that high-affinity NGF binding requires coexpression and binding to both the low-affinity NGF receptor and the tyrosine kinase trk gene product. These studies reveal a new growth factor receptor-mediated mechanism of cellular differentiation involving trk and the low-affinity NGF receptor.     

Effects of fluorinated dinitrobenzenes on erythrocyte membrane acetylcholinesterase

Zusammenfassung Die Acetylcholinesterase der Erythrozytenmembranen wurde mit 1, 5-Difluor-2, 4-dinitrobenzol stärker inaktiviert als mit 1-Fluor-2, 4-dinitrobenzol. Nach Difluordinitrobenzol-Behandlung war die restliche enzymatische Aktivität hitze- und harnstoffunempfindlich. Die Inaktivierung des Fermentes war konzentrations-, zeit- und temperaturabhängig.     

Mechanism of silk processing in insects and spiders

Silk spinning by insects and spiders leads to the formation of fibres that exhibit high strength and toughness. The lack of understanding of the protein processing in silk glands has prevented the recapitulation of these properties in vitro from reconstituted or genetically engineered silks. Here we report the identification of emulsion formation and micellar structures from aqueous solutions of reconstituted silkworm silk fibroin as a first step in the process to control water and protein-protein interactions. The sizes (100-200 nm diameter) of these structures could be predicted from hydrophobicity plots of silk protein primary sequence. These micelles subsequently aggregated into larger 'globules' and gel-like states as the concentration of silk fibroin increased, while maintaining solubility owing to the hydrophilic regions of the protein interspersed among the larger hydrophobic regions. Upon physical shearing or stretching structural transitions, increased birefringence and morphological alignment were demonstrated, indicating that this process mimics the behaviour of similar native silk proteins in vivo. Final morphological features of these silk materials are similar to those observed in native silkworm fibres.     

Contributions of microbial biofilms to ecosystem processes in stream mesocosms

In many aquatic ecosystems, most microbes live in matrix-enclosed biofilms and contribute substantially to energy flow and nutrient cycling. Little is known, however, about the coupling of structure and dynamics of these biofilms to ecosystem function. Here we show that microbial biofilms changed the physical and chemical microhabitat and contributed to ecosystem processes in 30-m-long stream mesocosms. Biofilm growth increased hydrodynamic transient storage-streamwater detained in quiescent zones, which is a major physical template for ecological processes in streams-by 300% and the retention of suspended particles by 120%. In addition, by enhancing the relative uptake of organic molecules of lower bioavailability, the interplay of biofilm microarchitecture and mass transfer changed their downstream linkage. As living zones of transient storage, biofilms bring hydrodynamic retention and biochemical processing into close spatial proximity and influence biogeochemical processes and patterns in streams. Thus, biofilms are highly efficient and successful ecological communities that may also contribute to the influence that headwater streams have on rivers, estuaries and even oceans through longitudinal linkages of local biogeochemical and hydrodynamic processes.     

Interconvertibility of molecular forms of 3'5' cyclic AMP phosphodiesterase of human platelets]

Three forms of cyclic AMP phosphodiesterase from human platelets are resolved upon sucrose gradient centrifugation : 2.5S (monomer), 4.8S (dimer) and 7S (tetramer). They are interconvertible and form an association-dissociation equilibrium depending on the concentration of enzyme. The dissociated form has a high Km for cyclic AMP (Km : 3-5.10(-4) M) whereas the associated form has a low Km (Km : 3-5.10(-5) M).