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Flavoproteins of the quiescin/sulfhydryl oxidase (QSOX) family catalyze oxidation of peptide and protein thiols to disulfides with the reduction of oxygen to hydrogen peroxide. We report here the molecular cloning of a new putative sulfhydryl oxidase cDNA, rQSOX-L (GenBank Accession no ), from adult rat brain and its expression studied by RT-PCR, Northern and Western blots in rat tissues. DNA-sequencing demonstrated the existence of two cDNAs in rat cortex, corresponding to a long transcript (rQSOX-L) and a short transcript (rQSOX-S) which differed by 851 nucleotides due to alternative splicing. The new transcript, rQSOX-L (3356 nucleotides), was specifically expressed in brain, hypophysis, heart, testis and seminal vesicle. The distribution of this variant is not homogeneous in the different tissues studied and suggests a complex gene regulation. The full-length rQSOX-L cDNA has an open reading frame of 2250-bp encoding a protein of 750 amino acids that contains a signal peptide sequence, a protein-disulfide-isomerase-type thioredoxin and ERV1-ALR domains and a long form specific C-terminal extension. The rQSOX-L protein is highly homologous to members of the sulfhydryl oxidase/Quiescin family and contains particularly two potential sites for N-glycosylation. This protein isoform was specifically detected in rat brain tissues in opposition to the low molecular form that was ubiquitous. Matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis of the immunoprecipitate tryptic fragments allowed the identification of rQSOX-L protein.

In studies of yeast flocculation it has been found that low concentrations of vanadium contained in sodium orthovanadate do not affect the growth and the cell-cell adhesion of the yeast Kluyveromyces bulgaricus, whereas high concentrations delay the growth of the yeasts and strongly inhibit flocculation. Moreover, higher sensitivity to Hygromycin B and calcofluor white was taken to imply altered cell wall integrity which is supported by compositional analysis of the extracted phosphopeptidomannans. Yeasts grown on sodium orthovanadate show a decrease in the percentage of phosphopeptidomannans and their compositions. It is proposed that the vanadium contained in sodium orthovanadate has a similar conformation to phosphorus and competes with phosphorus in phosphorylated compounds. The decrease of carbohydrate components and phosphorus linking to phosphopeptidomannans detected may alter their structure and modify ligand binding properties.