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Biomedical subjects

R Zenobi

Publications and source records attributed to R Zenobi.

29 records · Page 2Linked to original sources
PubMed1999

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for identifying the composition of labeled proteins.

Labeled proteins are extensively used in molecular biology and environmental science. The determination of the composition and label ratio is very important for monitoring the efficiency of their separation and purification. In this paper a novel method based on matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry was developed for this purpose. The results obtained for three commercial labeled proteins showed that they are mixtures of different conjugates. In some cases, the label ratio obtained by UV spectrometry and MALDI mass spectrometry was strikingly different. For fluorescent labels such as fluorescein isothiocyanate, MALDI mass spectrometry determines the number of covalently bound labels, whereas UV absorption yields both bound and adsorbed labels. For biotinylated proteins, label ratios obtained by the 4-hydroxyazabenzene-2'-carboxylic acid (HABA)-avidin method were found to be much smaller those determined by MALDI mass spectrometry. The HABA-avidin method may therefore not be suitable for the determination of biotin label ratios.

Biotin↗
PubMed1999

Matrix-assisted laser desorption/ionization mass spectra reflect solution-phase zinc finger peptide complexation.

The complexation between an 18-residue zinc finger peptide of CCHC type (CCHC = Cys-X2-Cys-X4-His-X4-Cys, X = variable amino acid) from the gag protein p55 of human immunodeficiency virus type 1 (HIV-1) and various transition metal ions was studied by means of circular dichroism spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A correlation between the complexation behavior in solution and in MALDI-MS could be established. It was shown that MALDI-MS is a fast method suitable for studying metal binding properties of zinc finger complexes.

Amino Acid Sequence↗
PubMed1998

MALDI mass spectrometry of dye-peptide and dye-protein complexes.

Immobilized sulfonate dyes are widely used for protein separation and purification, but the mode of interaction between the dye molecules and the proteins is largely unknown. Here we show that specific noncovalent dye-protein and dye-peptide complexes can be observed using MALDI mass spectrometry. We prove that the interaction is prodominantly electrostatic and that it involves protonated sites of the peptides and proteins, including the NH2 terminus, and deprotonated SO3 groups of the dyes. Furthermore, we show that MALDI-MS of such complexes with a nonacidic matrix, p-nitro-aniline, can be used to determine the number of accessible basic sites of a protein or peptide in its folded structure. Our results are in good agreement with measurements of the same property done with electrospray ionization.

Adrenocorticotropic Hormone↗
PubMed1998

Matrix-assisted laser desorption/ionization mass spectrometry of noncovalent protein-transition metal ion complexes.

Transition metal ion complexes with proteins and peptides are important in many areas of analytical and biological chemistry. We used positive and negative ion MALDI-MS to detect complexes with Cu and Ni ions, and show that the specific and non-specific transition metal ion-peptide complexes can be distinguished by the use of different analytical protocols. The pH dependent stability of these complexes is also reflected in the MALDI data. We further show that triple complexes of peptides or protein with chelated metal ions can be detected efficiently and rapidly by MALDI mass spectrometry. Such triple complexes play an important role in metal chelate affinity chromatography, where histidine containing biopolymers in particular are thought to bind metal-ligand complexes, depending on the oxidation state of the metal and the number of unoccupied coordination sites of the ligand.

Amino Acid Sequence↗
PubMed1994

Chemical analysis of cancer therapy photosensitizers by two-step laser mass spectrometry.

We have applied two-step laser mass spectrometry (L2MS) to the qualitative chemical analysis of porphyrin-derived photosensitizer dyes used for detection and photodynamic therapy of cancer. The only ionization technique applied so far to these low-volatility compounds had been fast atom bombardment (FAB), which suffers from problems associated with cluster formation of the porphyrins upon FAB ionization. From FAB and chromatography data, the existence of porphyrin dimers, trimers, and oligomers in commercial photosensitizers was concluded to be crucial for tumor localization, but it is possible that clustering or preformed van der Waals aggregates gave rise to these results. L2MS indicates that commercially available hematoporphyrin derivative and Photofrin II contain no detectable amounts of covalently bound porphyrin oligomers. Synthetic porphyrin dimers and trimers could be unambiguously detected by L2MS.

Lasers↗
PubMed1992

Organic compounds in the Forest Vale, H4 ordinary chondrite.

We have analyzed the H4 ordinary chondrite Forest Vale for polycyclic aromatic hydrocarbons (PAHs) using two-step laser mass spectrometry (L2MS) and for amino acids using a standard chromatographic method. Indigenous PAHs were identified in the matrices of freshly cleaved interior faces but could not be detected in pulverized silicates and chondrules. No depth dependence of the PAHs was found in a chipped interior piece. Amino acids, taken from the entire sample, consisted of protein amino acids that were nonracemic, indicating that they are terrestrial contaminants. The presence of indigenous PAHs and absence of indigenous amino acids provides support for the contention that different processes and environments contributed to the synthesis of the organic matter in the solar system.

Amino Acids↗
PubMedDate not supplied

Brighter near-field optical probes by means of improving the optical destruction threshold.

The optical destruction thresholds of conventionally etched and tube-etched near-field optical probes were measured. One of the main advantages of tube-etched tips is their smooth glass surface after taper formation. Presumably for this reason, a destruction limit of over 120 microJ was obtained, almost twice as large as that of the rougher, conventionally etched fibre probes. The use of additional adhesion layers (Ti. Cr, Co and Ni) between the glass surface and the aluminium coating produced, especially for tube-etched tips, a significant increase in the optical destruction threshold. With increasingly thin metal coatings, the use of a protection coating that prevents corrosion during aging is recommended. An additional increase in optical stability was achieved by applying mixed-metal coatings: alternating thin titanium and thick aluminium layers yielded fibre probes with superior properties that achieved average optical destruction thresholds of > 270 microJ. This is an increase in stability of > 400% compared with conventionally fabricated near-field optical tips.

Journal Article↗