Diffusion of the tracers Cu67, Ni66, and Zn65 in copper-rich solid solutions in the system Cu-Ni-Zn

Tracer diffusion coefficients were determined for the three isotopes, Zn⁶⁵, Cu⁶⁷, and Ni⁶⁶, in homogeneous Cu-Ni-Zn binary and ternary alloys, to 30 pct Ni and Zn, and pure copper as a function of composition and as a function of temperature, within about 250°C of the solidus surface. Activation energies andD ₀ factors were determined as functions of composition from these measurements. It is found that as the composition plane is traversed in the general direction from high nickel compositions on the copper-nickel binary to high zinc concentrations on the copper-zinc binary,i.e., as nickel is replaced by zinc, the diffusivity of all three tracers increases, and the activation energy for diffusion decreases. The total change in diffusivity across the composition plane is about two orders of magnitude. The three diffusivities are always in the order:D*_Zn >D*_Cu >D*_Ni, with the ratio being 9∶3∶1 at 900°C for all compositions. The three activation energies are usually in the orderQ*_Ni >Q*_Cu >Q*_Zn. These results are shown to be consistent with atom size and electron-to-atom concentrations of the three species in this alloy system. K. J. ANUSAVICE, formerly Graduate Student, Department of Materials Engineering, University of Florida, Gainesville, Fla.     

The Oms66 (p66) protein is a Borrelia burgdorferi porin

In this study we report the purification and characterization of a 66-kDa protein, designated Oms66, for outer membrane-spanning 66-kDa protein, that functions as a porin in the outer membrane (OM) of Borrelia burgdorferi. Oms66 was purified by fast-performance liquid chromatography and exhibited an average single-channel conductance of 9.62 +/- 0.37 nS in 1 M KCl, as evidenced by 581 individual insertional events in planar lipid bilayers. Electrophysiological characterization indicated that Oms66 was virtually nonselective between cations and anions and exhibited voltage-dependent closure with multiple substates. The amino acid sequence of tryptic peptides derived from purified Oms66 was identical to the deduced amino acid sequence of p66, a previously described surface-exposed protein of B. burgdorferi. Purified Oms66 was recognized by antiserum specific for p66 and serum from rabbits immune to challenge with virulent B. burgdorferi, indicating that p66 and Oms66 were identical proteins and that Oms66/p66 is an immunogenic protein in infected rabbits. In a methodology that reduces liposomal trapping and nonspecific interactions, native Oms66 was incorporated into liposomes, confirming that Oms66 is an outer membrane-spanning protein. Proteoliposomes containing Oms66 exhibited porin activity nearly identical to that of native, purified Oms66, indicating that reconstituted Oms66 retained native conformation. The use of proteoliposomes reconstituted with Oms66 and other Oms proteins provides an experimental system for determinating the relationship between conformation, protection, and biological function of these molecules.