Reversed-phase high-performance liquid chromatographic amino acid analysis of phosphoproteins electroblotted onto a polyvinylidene difluoride membrane using dimethylaminoazobenzene sulfonyl chloride as derivatizing reagent

Development of a Fluorescent Labeling Reagent for Determination of Proline and Hydroxyproline in Myeloma Patient Plasma by HPLC-FLD

A fluorescent derivatization reagent, 3,6-dimethoxy-9-phenyl-9H-carbazole-1-sulfonyl chloride (DPCS-Cl), previously designed, synthesized and developed for amino acids labeling, is here employed. It was used as a pre-column derivatization reagent for the determination of proline (Pro) and hydroxyproline (Hyp) with high-performance liquid chromatography. Both of the analytes were labeled with DPCS-Cl at 60°C for 30 min. The optimized concentration of DPCS-Cl was 25 µg mL^-1 and the molar ratio of analytes to DPCS-Cl was 1:6. Excitation wavelength of 318 nm and emission wavelength of 440 nm were selected for the fluorescence detection. For Pro and Hyp, the linear correlation coefficients were all >0.999; the linear ranges of calibration curve were all 5.0 nmol L^-1 to 5.0 μmol L^-1; the detection limits were 20.0 and 10.0 fmol, respectively; the intra-day and inter-day relative standard deviations were 2.6-3.3% and 3.5-4.6%, respectively. This reagent was applied to the determination of Pro and Hyp in plasma of myeloma patients with its merits of high efficiency of derivatization, stability of the derivatives and high sensitivity.

Biochemical and molecular characterization of NADP-glutamate dehydrogenase from the ectomycorrhizal fungus Tuber borchii

• NADP-glutamate dehydrogenase (NADP-GDH) from Tuber borchii was purified and the corresponding gene was cloned in order to elucidate the physiological role of the enzyme in this ectomycorrhizal fungus. • NADP-GDH was purified using an anion-exchange column followed by affinity chromatography. The complete gene was cloned from a 30-d-old-mycelium cDNA library and characterized. • T. borchii NADP-GDH appears to be physically and kinetically similar to those from other fungi and the deduced amino acid sequence of the gdh gene showed a significant similarity to other fungal NADP-dependent GDHs. Biochemical and Northern blotting analyses carried out with mycelia grown on different nitrogen sources clearly showed that the regulation of T. borchii NADP-GDH in response to different nitrogen sources was markedly different from the responses of the NADP-GDHs of other ascomycetes. Northern blotting analyses highlighted that the gdh gene was also expressed in the symbiotic phase. • The biochemical and molecular data suggest that the fungal NADP-GDH contributes to the primary nitrogen metabolism in the ectomycorrhizal tissues.

Identification of Tuber borchii Vittad. mycelium proteins separated by two-dimensional polyacrylamide gel electrophoresis using amino acid analysis and sequence tagging

This paper reports the first results in the proteome analysis of Tuber borchii Vittad. mycelium, an ectomycorrhizal fungus poorly defined genetically, but known for its generation of edible fruit bodies known as white truffles. Employing isoelectric focusing on immobilized pH gradients, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we obtained an electropherogram presenting over 800 spots within the window of isoelectric points (pI) 3.5-9 and a molecular mass of 10-200 kDa. Different reducing agents were tested in the sample preparation buffers, and the standard lysis buffer plus 2% w/v polyvinylpolypyrrolidone allowed the best solubilization and resolution of the proteins. The T. borchii proteins separated in micropreparative gels were electroblotted onto polyvinylidene difluoride membranes and visualized by Coomassie staining. Twenty-three proteins were excised and analyzed by the combination of amino acid and N-terminal analysis. One protein was identified by matching its amino acid composition, estimated isoelectric point and molecular mass against the SWISS-PROT and EMBL databases. Four spots were successfully tagged by Edman microsequencing but no homologous sequences were found in databases.

Dehydroascorbic acid irreversibly inhibits hexokinase activity

The oxidized form of vitamin C (dehydroascorbic acid, DHA) completely and irreversibly inactivates recombinant human hexokinase type I, in a pseudo-first order fashion. The inactivation reaction occurs without saturation, indicating that DHA does not form a reversible complex with hexokinase. Further characterization of this response revealed that the inactivation does not require oxygen and that dithiothreitol, while able to prevent the DHA-mediated loss of enzyme activity, failed to restore the activity of the DHA-inhibited enzyme. Inactivation was not associated with cleavage of the peptide chain or cross-linking. The decay in enzymatic activity was however both dependent on deprotonation of a residue with an alkaline pKa and associated with covalent binding of DHA to the protein. In addition, inactivation of hexokinase decreased or increased, respectively, in the presence of the substrates glucose or MgATP. Finally, amino acid analysis of the DHA-modified hexokinase revealed a decrease of cysteine residues. Taken together, the above results are consistent with the possibility that covalent binding of the reagent with a thiol group of cysteine is a critical event for the DHA-mediated loss of hexokinase activity.

Protein analysis by mass spectrometry and sequence database searching: tools for cancer research in the post-genomic era

The post-genomic era is characterized by the deposition of sequence information for entire genomes in databases. Currently, besides the protein sequences for known human proteins, there are partial sequences from thousands more human proteins for which no biological function has been assigned. A powerful new tool for the unambiguous identification and characterization of gel-separated proteins is accomplished by the combination of mass spectrometry and sequence database searching. This combination provides the cancer biologist with the ability to (i) identify the potential protein:protein associations and (ii) fully characterize function-critical post-translational modifications, both directly from silver-stained polyacrylamide gels. In this report we describe the application of tandem mass spectrometry and database searching to two problems which are prototypical for cancer research and indeed for biomedical research in general. The first is the identification of gel-separated, low abundance proteins based on amino acid sequence composition following coimmunoprecipitation with the human apoptosis inhibitor protein BclX(L). The second is the determination of the precise sites of phosphorylation of the human regulatory protein 4E-BP1, which controls mRNA translation.