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Isotope dilution analysis is proposed for the determination of selenomethionine (SeMet) in Se-enriched yeast material by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) using a 77 Se-enriched selenomethionine spike obtained by yeast growth on a 77 Se-rich culture medium. Different methods of yeast enrichment with selenium were evaluated to determine the most effective one. The use of two different culture media, amount of selenium added, amount of carbon source (glucose) and harvest time were evaluated in order to characterize the total selenium incorporated by the yeast cells. The yeast proteins were hydrolysed with protease XIV, and the isotopically enriched SeMet isolated by anion exchange chromatography. The isotopic composition of the SeMet in the spike solution was determined by online HPLC-ICP-MS and reverse isotope dilution was used for the characterization of the spike by means of a natural SeMet standard. In the analysis of the Se-enriched yeast material, the sample was spiked with 77 Seenriched SeMet, and hydrolyzed with a non-specific enzyme (protease XIV) at 37 uC for 20 hours or using an ultrasonic probe for 1 min. Both 78 Se/ 77 Se and 80 Se/ 77 Se isotope ratios were measured by ICP-MS with collision and reaction cell after the separation of selenomethionine by HPLC. The method was applied to the determination of selenomethionine in a candidate yeast reference material (SEAS project), and the results obtained were in agreement with those reported by other laboratories.

A protein of 34 kDa (Nx) was induced in vitro by the infection of fish cell cultures with the rhabdovirus agent of viral haemorrhagic septicaemia (VHS) of the trout. This protein only appeared as a major component in concentrated or intracellular labeled VHS virus but not in purified VHS or in the related infectious haematopoietic necrosis virus. That Nx protein is antigenically related to the nucleoprotein of purified virus was shown by its reaction with four anti-nucleoprotein monoclonal antibodies (at least 3 of them reacting non competitively against different epitopes) and by immunoprecipitation with polyvalent international reference sera. The Nx protein was shown to be specifically associated with free non-infective particles isolated by ultracentrifugation which were confirmed to be nucleocapsids by electron microscopy.

Five VHSV isolates from different host species and Spanish geographical locations and three viral haemorrhagic septieaemia virus (VHSV) international reference serotypes (Fj, FT and 23-75) were studied by several characterized monoclonal antibodies (MAbs) including a neutralizing MAb to four structural proteins of VHSV. We report here the lack of reaction between anti-Ml and some of the isolates of VHSV and the homogeneity of most of the isolates with respect to the MAbs tested. The reagents obtained will improve diagnostic tests which currently use polyclonal antibodies.