ElaC is a widespread gene found in eubacteria, archaebacteria, and mammals with a highly conserved sequence. Two human ElaC variants were recently associated with cancer ( Tavtigian 72, 169 -179). Analysis of the primary sequence indicates homology to an arylsulfatase and predicts a metallo-␤-lactamase fold. At present, no ElaC gene product has been investigated. We cloned the Escherichia coli ElaC gene and purified the recombinant gene product. An enzymatic analysis showed that ElaC does not encode an arylsulfatase but rather encodes a phosphodiesterase that hydrolyzes bis(p-nitrophenyl)phosphate with a k cat of 59 s ؊1 and K of 4 mM. Kinetic analysis of the dimeric enzyme revealed positive cooperativity for the substrate bis(p-nitrophenyl)phosphate with a Hill coefficient of 1.6, whereas hydrolysis of the substrate thymidine-5-p-nitrophenyl phosphate followed Michaelis-Menten kinetics. Furthermore, the enzyme is capable of binding two zinc or two iron ions. However, it displays phosphodiesterase activity only in the zinc form. The metal environment characterized by zinc K-edge xray absorption spectroscopy was modeled with two histidine residues, one carboxylate group, and 1.5 oxygen atoms. This corresponds to the coordination found in other metallo-␤-lactamase domain proteins. Phosphodiesterase activity is strongly dependent on the presence of zinc. These results identify the currently unassigned gene product ElaC to be a novel binuclear zinc phosphodiesterase.

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There is an error in the list of references cited and one reference is missing. The correct references are:Niecke M, Heid M, Krüger A (1999) Correlations between melanin pigmentation and element concentration in feathers of white-tailed eagle. J Ornithol 140:355-362 Niecke M (2000) Ist die selektive Anreicherung von Elementen in melaninhaltigen Vogelfedern ein generelles Phänomen? Beitr Gefiederkd Morphol Vögel 6:36-43The online version of the original article can be found at http:// dx.

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Abrasive joint replacement material that accumulates in the tissue induces reciprocal effects between prosthesis material and organism. Since the limitations of brightfield and polarized light microscopy for foreign body analysis are well known, a method was applied that ensures the detailed histological assessment of nonbirefringent particles in periprosthetic soft and hard tissue. Cemented and cementless interface regions of five selected autopsy hip implant cases (2 x Endo-Modell Mark III, LINK, 1 x St. Georg Mark II, LINK, Germany; 2 x Spongiosa Metal II, ESKA, Germany) were viewed under darkfield illumination and subsequently analyzed with proton-induced X-ray emission (PIXE). Eight autopsy cases without implants served as controls. Using darkfield illumination technique, metallic particles became visible as luminous points under the microscope. The majority of particles in the samples from the cemented cases were degradation products of radiopaque bone cement. There was minimal evidence of metallic alloy particles in the soft tissues. However, a considerable quantity of heavy metal cobalt (Co) was found in the periprosthetic mineralized bone tissue, which was not observed in the controls. The periprosthetic concentration of cobalt ranged from 38 to 413 ppm. The findings demonstrate a correlation between cobalt concentration, time since implantation, and distance from the implant. Darkfield microscopy associated with PIXE enables a detailed histological assessment of metal particles in the tissue. In an effort to optimize biomechanics, implant design and implantation techniques, the contamination of soft and hard tissue with heavy metal degradation products deserves similar attention in terms of alloy assortment.