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Core/shell1/shell2/shell3 structured NaGdF4:Nd/NaYF4/NaGdF4:Nd,Yb,Er/NaYF4 nanocrystals were well designed and synthesized, each of the parts assume respective role and work together to achieve dual-mode upconverting (UC) and downconverting (DC) luminescence upon the low heat effect 800-nm excitation. Nd3+, Yb3+, Er3+ tri-doped NaGdF4:Nd,Yb,Er UC layer [NIR (800 nm)-to-Visible (540 nm)] with a constitutional efficient 800 nm excitable property were achieved for the in-vitro bioimaging with low auto-fluorescence and photo-damage effects. Moreover, typical NIR (800 nm)-to-NIR (860-895 nm) DC luminescence of Nd3+ has also been realized with this designed nanostructure. Due to the low heat effect, high penetration depth of the excitation and the high efficiency of the DC luminescence, the in-vivo high contrast DC imaging of a whole body nude mouse was achieved. We believe that such dual-mode luminescence NCs will open the door to engineering the excitation and emission wavelengths of NCs and will provide a new tool for a wide variety of applications in the fields of bioanalysis and biomedical. [ABSTRACT FROM AUTHOR]

Anticoagulation factor I (ACF I) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein that binds in a Ca2+-dependent fashion with marked anticoagulant activity. The thermodynamics of the binding of alkaline earth metal ions to ACF I and the effects of alkaline earth metal ions on the guanidine hydrochloride (GdnHCl)-induced unfolding of ACF I and the binding of ACF I to FXa were studied by isothermal titration calorimetry, fluorescence, circular dichroism, and surface plasmon resonance, respectively. The results indicate that the ionic radii of the cations occupying Ca2+-binding sites in ACF I crucially affect the binding affinity of ACF I for alkaline earth metal ions as well as the structural stability of ACF I against GdnHCl denaturation. Sr2+ and Ba2+, with ionic radii larger than the ionic radius of Ca2+, can bind to Ca2+-free ACF I (apo-ACF I), while Mg2+, with an ionic radius smaller than that of Ca2+, shows significantly low affinity for the binding to apo-ACF I. All bindings of Ca2+, Sr2+, and Ba2+ ions in two sites of ACF I are mainly enthalpy-driven and the entropy is unfavorable for them. Sr2+-stabilized ACF I exhibits slightly lower resistance to GdnHCl denaturation than Ca2+–ACF I, while Ba2+-stabilized ACF I exhibits much lower resistance to GdnHCl denaturation than Ca2+–ACF I. Mg2+ and Sr2+, with ionic radii close to that of Ca2+, can bind to FXa and therefore also induce the binding of ACF I to FXa, whereas Ba2+, with a much larger ionic radius than Ca2+, cannot support the binding of ACF I with FXa. Our observations suggest that bindings of Ca2+, Sr2+, and Ba2+ ions in two sites of ACF I increase the structural stability of ACF I, but these bindings are not essential for the binding of ACF I with FXa, and that the binding of Mg2+, Ca2+, and Sr2+ ions to FXa may be essential for the recognition between FXa and ACF I. [ABSTRACT FROM AUTHOR]

Abstract  The serum albumin is the most abundant protein in blood plasma and the iron is essential for many cellular processes. However, the interaction between Fe3 and haem-free serum albumin remains unclear. Here we provide evidence for the fact that haem-free BSA possesses one specific Fe3+binding site. The binding of Fe3 to BSA results in a significant quenching of the Trp fluorescence of BSA. The average apparent dissociation constant value for the interaction of Fe3 and BSA is 3.46 × 10−8 ± 3 × 10−10 M at 37 °C and 3.30 × 10−8 ± 5 × 10−10 M at 25 °C, respectively, as determined by fluorescence titration. Addition of 50 μM Fe2 to 1 μM BSA results in an obvious hysteretic effect on the fluorescence of BSA. The time-dependent fluorescence quenching of BSA by Fe2 is not caused by the Fe2+induced conformational change of BSA, but the oxygen-dependent oxidation of Fe2 to Fe3. Fe2 undergoes an oxygen-dependent oxidation to Fe3 under aerobic conditions, which is accelerated by the interaction of BSA with Fe3 and extensively inhibited under anaerobic conditions. The results suggest that BSA may take part in non-transferrin bound iron transfer. [ABSTRACT FROM AUTHOR]

Abstract??Agkisacutacin isolated from the venom ofAgkistrodon acutusis a coagulation factor IX / coagulation factor X-binding protein with marked anticoagulant- and platelet-modulating activities. Ca2+ion-induced stabilization and refolding of Agkisacutacin have been studied by following fluorescent measurements. Ca2+ions not only increase the structural stability of agkisacutacin against GdnHCl denaturation, but also induce its refolding. The GdnHCl-induced unfolding of the apo-agkisacutacin and the purified agkisacutacin is a single-step process with no detectable intermediate state. Ca2+ions play an important role in the stabilization of the structure of agkisacutacin. Ca2+-stabilized agkisacutacin exhibits higher resistance to GdnHCl denaturation than the apo-agkisacutacin. It is possible to induce refolding of the unfolded apo-agkisacutacin merely by adding 1?mM Ca2+ions without changing the concentration of the denaturant. The kinetic result of Ca2+-induced refolding provides evidences for that agkisacutacin consists of at least two refolding phases and the first phase of Ca2+-induced refolding should involve the formation of the compact Ca2+-binding site regions, and subsequently, the protein undergoes further conformational rearrangements to form the native structure. [ABSTRACT FROM AUTHOR]