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The different behaviour of two isozymes (IsoA and IsoB) of catechol 1,2-dioxygenase (C 1,20) from Acinetobacter radioresistens S13 on a hydrophobic interaction, Phenyl-Sepharose chromatographic column, prompted us to investigate the role of superficial hydrophobicity on structural-functional aspects for such class of enzymes. The interaction of 8-anilino-1-naphtalenesulphonate (ANS), a fluorescent probe known to bind to hydrophobic sites in proteins, revealed that the two isoenzymes have a markedly different hydrophobicity degree although a similar number of hydrophobic superficial sites were estimated (2.65 for IsoA and 2.18 for IsoB). ANS is easily displaced by adding the substrates catechol or 3-methylcatechol to the adduct, suggesting that the binding sites are in the near surroundings of the catalytic clefts. The analysis of the hydropathy profiles and the possible superficial cavities allowed to recognize the most feasible region for ANS binding. The lower hydrophobicity detected in the near surroundings of the catalytic pocket of IsoB supports its peculiarity to lose the catalytic metal ions more easily than IsoA. As previously suggested for other metalloenzymes, the presence of more hydrophilic and/or smaller residues near to the active site of IsoB is expected to increase the metal ligands mobility thus increasing the metal ion dissociation rate constants, estimated to be 0.078 h(-1) and 0.670 h(-1) for IsoA and IsoB respectively.

A previously described conjugate of 8-hydroxyquinoline and bovine serum albumin was complexed with lead(II), (8-hydroxyquinoline to metal ion ratio 2:1) and used as an immunogen to produce polyclonal antibodies against lead in chickens. Antibodies obtained from a first blood sample during a standard immunisation procedure showed very promising features (dynamic range of the assay was 1 to 1000 ng l(-1)). Nevertheless, proceeding with the immunisation caused a complete loss of the recognition of the complex. A modified brief immunisation procedure was carried out and, in this case, the immunogen proved to be sufficiently stable in vivo to produce antibodies that selectively bound to the lead(II) complex (in the same 2:1 ratio used as an immunogen). Since the antiserum obtained cannot reach the same performance levels as the first one, standard curves were obtained by adding the free 8-hydroxyquinoline to the solution, which enables 2:1 complexes to be more easily formed. Cross-reactivity and dependence from buffer were investigated, showing at least 10-fold lower binding to non-target divalent metal ions compared to lead(II). MES buffer (pH = 6.0) gave more sensitive but very imprecise curves, whereas Tris (pH = 8.5) allows higher precision but lower sensitivity to be observed.

In our work we performed a combinatorial solid-phase synthesis in aqueous medium to prepare peptide libraries from which to select an amino acid sequence with binding properties towards aflatoxins. We used polystyrene beads, functionalised with carboxylic groups as solid support and eight amino acids as monomers. During the first step 64 different sequences of two amino acids were prepared by exploiting the principles of combinatorial chemistry; then the binding properties of all sequences towards aflatoxin B(1 )were checked. We determined binding constants towards aflatoxin B(1) and towards aflatoxins B(2), G(1) and G(2). Results were promising, so we prepared a new library by using the selected dipeptide as the starting solid phase. After selecting the best tetrapeptide sequences, we determined binding constants towards the quoted aflatoxins. We obtained binding constants ( K>10(4) M(-1)) similar to those shown by human serum albumin for similar compounds. Preliminary studies on an extraction column were promising for the development of an SPE system and for its application in food matrices.

One of the goals of the new automated immunoassay analysers is to perform direct analysis in complex matrices thus overcoming traditional limits of homogeneous immunoassays: reduced sensitivity and ability to determine above all proteins and antibodies. The aim of this work was to demonstrate the feasibility of quantitative homogeneous immunoassay for small analytes in a complex matrix with a rapid and easy assay by exploiting an agglutination reaction. We studied the steroid hormone progesterone, and used new technology, the Copalistrade mark, which uses a special optical-sizing flow particle analysis and a semiconductor laser as a light source. We used polystyrene microbeads coated with the antigen as markers and put them in competition with the analyte in solution for the analytical antiserum. We synthesised and tested different conjugates of progesterone-bovine serum albumin, optimising all the experimental parameters. We performed a short pre-treatment of the serum and we obtained a detection limit of 0.011 ngcm(-3) and a working range between 0.026 and 43 ngcm(-3). We estimated human serum specimens and, with minor experimental revisions, the amounts of progesterone found agreed accurately with AutoDELFIAtrade mark analysis. The recoveries are good. All the experimental steps are easy, rapid and enable us to process many samples contemporarily.