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Plants have developed a constitutive defense system against pest attacks, which involves the expression of a set of inhibitors acting on heterologous amylases of different origins. Investigating the soluble protein complement of the hulled wheat emmer we have isolated and characterized a heterotetrameric α-amylase inhibitor (ETI). Based on mass spectrometry data, it is an assembly of proteins highly similar to the CM2/CM3/CM16 found in durum wheat. Our data indicate that these proteins can also inhibit exogenous α-amylases in binary assemblies. The calculated dissociation constants (K(i)) for the pancreatic porcine amylase- and human salivary amylase-ETI complexes are similar to those found in durum and soft wheat. Homology modeling of the CM subunits indicate structural similarities with other proteins belonging to the cereal family of trypsin/α-amylase inhibitors; a possible homology modeled structure for a tetrameric assembly of the subunits is proposed.

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A complete two-dimensional imaging system based on a silicon monolithic array of 60 single-photon counters is presented. The fabricated solid-state array is rugged and operates at low voltages. Detection efficiency is higher than 40% in the visible range, and cross talk among 50 microm pixels is lower than 10(-4). The complete system provides a maximum throughput of 20 kframes/s with truly parallel readout and nanosecond gating, thanks to the use of an integrated active quenching circuit for each pixel of the array. We report optical and electrical characterizations of the whole imaging system.

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The structural characterisation of a synthetic peptide reproducing the sequence 1-30 of Par j 1.0101, a major allergenic protein present in the pollen of Parietaria judaica, by combined use of chemical and enzymatic cleavage, reversed-phase high-performance liquid chromatography and electrospray ionisation mass spectrometry (ESI-MS), is described. Direct ESI-MS of the synthetic peptide after reaction with methyl iodide showed that the product is a mixture of two peptides: one form in which two out of the four cysteine residues present in the sequence are oxidised and a minor amount of another form in which all the cysteines are fully reduced. It was ascertained, using the combined procedure indicated above and without prior separation of the two species, that the disulphide bond in the partially oxidised form is located between cysteines 29 and 30. These results show the usefulness of this approach for characterising synthetic peptides containing multiple cysteine residues in the sequence.

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In order to improve the accuracy in the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) determination of the molecular mass of cyanogen bromide (CNBr) fragments of proteins, the post-cleavage reaction of these fragments with tris(hydroxymethyl)aminomethane (Tris) was tested. Mixtures of homoserine and homoserine lactone peptide fragments originating from CNBr cleavage of cytochrome c, lysozyme and human serum albumin were used as model compounds. Reaction of these fragments with Tris converts quantitatively the homoserine lactone ending peptides into the corresponding amides, leaving unmodified the homoserine ending forms. Thus, pairs of fragments which differ by 103 Da are formed. In contrast to the unmodified CNBr mixtures of peptides, which, due to the overlap of the signals of the free homoserine and homoserine lactone forms, produce unresolved peaks in the high mass region of the MALDI spectra, these pairs of fragments give resolved doublets of peaks up to a mass of 20000 Da. This permits accurate determination of the molecular mass of the fragments. Using this procedure, differences less than 5 Da with respect to the calculated values were obtained for the fragments examined.

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An electrospray ionisation (ESI) mass spectrometric method for the determination of the free energy (DeltaG) of unfolding of proteins is described. The method was tested using three blue copper proteins: wild type azurin, Cys-3Ala/Cys-26Ala (C3A/C26A) azurin mutant and wild-type amicyanin. The time course of the denaturation process of the proteins dissolved in methanol/water (50:50, v/v, pH 3.5) was followed by recording ESI mass spectra at time intervals. The spectra showed two series of peaks, corresponding to the native holo-protein and the unfolded apo-protein. From the intensity ratio of these two series of peaks at increasing time and at equilibrium, the free energy for the unfolding process for the three proteins could be determined. To evaluate the reliability of the thermodynamic data obtained by the ESI mass spectrometric approach, the denaturation process was followed by UV-VIS spectroscopy. The two sets of data obtained by these independent methods were in good agreement indicating that the ESI-MS approach can be used to obtain reliable quantitative information about the protein unfolding process. In principle, this approach can be applied to other proteins and requires very low amounts of sample, due to the intrinsic sensitivity of mass spectrometry. This may prove particularly useful when the amount of sample available prevents the use of current methods.

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The isolation by gel-permeation chromatography on Sephadex G-100 of a non-covalent complex of Cibacron Blue F3G-A (CB) with human serum albumin (HSA) is described. The complex presents a molar ratio of 3:1 CB-HSA and can be re-chromatographed under the same conditions without modification of its composition. However, complete dissociation occurs when the complex is chromatographed in the presence of denaturing agents. The effect of pH on the molar composition of the complex was also investigated by gel-permeation chromatography. Analogous complexes between CB and A and C cyanogen bromide fragments of unreduced HSA were also isolated by gel-permeation chromatography on Sephadex G-50. They present a molar ratio of 0.8:1 and 1.3:1 CB-protein for fragments A and C, respectively. These results suggest that two of the three molecules of CB bound to HSA may be located in the hydrophobic pocket corresponding to subdomain IIA, with the other molecule in the hydrophobic site corresponding to subdomain IIIA. The UV-Vis and dichroic circular spectra of the isolated complexes are reported.

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The determination of the tryptic peptide mapping of sequence 299-585 (cyanogen bromide fragment A) of human serum albumin (HSA) by chemical and enzymatic cleavages and combined use of HPLC and FAB-MS is described. Reduction and carboxymethylation of A gave four subfragments which were separated by HPLC and digested with trypsin. Tryptic fragments were separated by HPLC and identified by FAB-MS. A total coverage of about 95% of the entire sequence was obtained. Tryptic fragments not identified include mostly single amino acids and very hydrophilic peptides which were absent in the chromatograms. The high reproducibility of the experiments and the satisfactory yield of the tryptic fragments identified demonstrate the great potential of the combined use of HPLC separation and FAB-MS analysis for the structural investigation of HSA.

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The structural characterization of two synthetic model peptides of the cI434 repressor is described. Unequivocal determination of the structure was achieved by means of electrospray ionization mass spectrometry of the intact peptides and by fast atom bombardment mass spectrometric identification of complementary peptide fragments obtained by tryptic and chymotrypic digestion and partial separation by reversed-phase high-performance liquid chromatography. The results show the potential of this approach for characterizing synthetic peptides of relatively high molecular weight.

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The determination of the tryptic peptide mapping of sequence 1-298 of human serum albumin (HSA) by chemical and enzymatic cleavage and combined use of high-performance liquid chromatography (HPLC) and fast-atom bombardment mass spectrometry (FAB-MS) is described. A total coverage of about 75% of the entire sequence was obtained. Unidentified fragments included some peptides which were not present in the chromatograms because of their extreme hydrophobic or hydrophilic character, as indicated by the calculated retention times. Due to the high reproducibility of the experiments and to the satisfactory yield of the tryptic fragments identified, the combined use of HPLC and FAB-MS appears to possess great potential for structural investigation of HSA.

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Sodium [N-(1,5-dimethyl-3-oxo-2-phenylpyrazolin-4-yl)-N-methylamino] methanesulfonate (dipyrone) cannot be detected as such in biological fluids since absorption is preceded by hydrolysis to 4-methylaminoantipyrine, which is actually absorbed and further metabolized. In the present work standardized TLC Rf values and gas chromatographic retention indices for the four main urinary metabolites of dipyrone were determined. Inclusion of these parameters in the principal component analysis "scores plot" allows dipyrone to be included as a possible candidate in the not oriented search for unknown drug assumption in cases of overdose intoxication or poisoning.

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Five peptides containing the amino acids alanine, asparagine, histidine, isoleucine and tryptophan were investigated by partial methanolysis and fast atom bombardment mass spectrometry in order to examine the behaviour of these amino acid residues under the conditions employed in the methanolytic step. The results obtained confirm that partial methanolysis prior to mass analysis increases considerably the content of sequence information in the mass spectra and that no secondary reactions occur in the residues of the amino acids now investigated, with the exception of the esterification of the glutamic acid carboxyl group and partial conversion of the asparagine amide group in the corresponding methyl ester.

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The possibility of obtaining sequence information on peptides by partial methanolysis with 5 N HCl in dry methanol and subsequent fast atom bombardment (FAB) of the resulting mixture was investigated. This procedure was tested using four peptides of different size and amino acid composition. The results obtained demonstrate that this approach is effective in producing FAB spectra containing more sequence information than the spectra of the untreated peptides. For the compounds investigated the spectra contain enough information to unequivocally reassemble the original sequence.

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Site-directed covalent modification of proteins is currently used to study the molecular structure of enzyme active sites. Radioactive labels together with protein sequencing by Edman degradation have been previously employed to identify the site of modification. One drawback of such a procedure is that most reagents are not commercially available in radioactive form. Moreover, the covalent bond formed upon reaction of the label with the protein may be labile under the conditions of Edman degradation. By combining reverse-phase high-performance liquid chromatography (RP-HPLC) and fast atom bombardment (FAB) mass spectrometry, we have been able to identify the modified sites of horse heart cytochrome c after reaction with iodine. By using this procedure it has been possible to ascertain that, among the four tyrosines contained in the sequence of horse heart cytochrome c, only tyrosine 74 is converted into the monoiodinated derivative. The data demonstrate also the absence of unwanted secondary reactions. The technique avoids the use of radioactive materials and prevents losses of the label since Edman degradation is not required to identify the modified peptides. These results indicate that FAB mass spectrometry along with RP-HPLC is potentially a powerful technique to study chemical modifications of proteins.

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