High-performance liquid chromatographic-fluorimetric assay for cathepsin A (lysosomal protective protein) activity

Selective and sensitive determination of peptides using 3,4-dihydroxyphenylacetic acid as a fluorogenic reagent

A novel fluorescence (FL) reaction for N-terminal Gly-containing peptides has been developed using 3,4-dihydroxyphenylacetic acid (3,4-DHPAA). The reaction of the peptides with 3,4-DHPAA was carried out in borate buffer (pH 8.0) in the presence of sodium periodate at 37°C for 10 min, and the FL was measured with a spectrofluorimeter at the excitation and emission wavelengths of 370 nm and 465 nm, respectively. The 3,4-DHPAA reagent generated particularly strong FL for peptides containing Gly at their N-termini. When various other bio-substances, such as amino acids, sugars, nucleic bases, nucleotides, and proteins, were reacted with 3,4-DHPAA, no FL was observed. Under optimized reaction conditions, the lower detection limit of 0.25 μmol L(-1) was obtained for the N-terminal Gly-containing peptides of Gly-Pro (GP) and Gly-Pro-Pro (GPP), which gave 3 times greater FL intensity than that observed for the reagent blank. The proposed reaction with 3,4-DHPAA as a fluorogenic reagent is selective and sensitive for the detection of N-terminal Gly-containing peptides, and therefore, this method could be a useful tool for the determination of these particular oligopeptides.

Selective Determination of Tryptophan-containing Peptides through Precolumn Derivatization and Liquid Chromatography Using Intramolecular Fluorescence Resonance Energy Transfer Detection

A selective and sensitive fluorometric determination method for native fluorescent peptides has been developed. This method is based on intramolecular fluorescence resonance energy transfer (FRET) detection in a liquid chromatography (LC) system following precolumn derivatization of the amino groups of tryptophan (Trp)-containing peptides. In this detection process, we monitored the FRET from the native fluorescent Trp moieties (donor) to the derivatized fluorophore (acceptor). From a screening study involving 10 fluorescent reagents, we found that o-phthalaldehyde (OPA) generated FRET most effectively. The OPA derivatives of the native fluorescent peptides emitted OPA fluorescence (445 nm) through an intramolecular FRET process when they were excited at the excitation maximum wavelength of the Trp-containing peptides (280 nm). The generation of FRET was confirmed through comparison with the analysis of a non-fluorescent peptide (C-reactive protein fragment (77 - 82)) performed using LC and a three-dimensional fluorescence detection system. We were able to separate the OPA derivatives of the Trp-containing peptides when performing LC on a reversed-phase column. The detection limits (signal-to-noise ratio = 3) for the Trp-containing peptides, at a 20-microL injection volume, were 41 - 180 fmol. The sensitivity of the intramolecular FRET-forming derivatization method is higher than that of the system that takes advantage of the conventional detection of OPA derivatives. Moreover, native non-fluorescent amines and peptides in the sample monitored at FRET detection are weaker than those of conventional fluorescence detection.

High-performance liquid chromatographic-fluorimetric assay of chymotrypsin-like esterase activity

A sensitive and reproducible assay for the determination of chymotrypsin-like esterase activity is reported. This method is based on fluorimetric detection of a dansylated amino acid, 5-dimethylaminonaphthalene-1-sulfonyl-L-phenylalanine, enzymatically formed from the substrate 5-dimethylaminonaphthalene-1-sulfonyl-L-phenylalanine ethyl ester, after separation by high-performance liquid chromatography using a C18 reversed-phase column and isocratic elution. This method is sensitive enough to measure 5-dimethylaminonaphthalene-1-sulfonyl-L-phenylalanine at concentrations as low as 40 pmol/ml, yields highly reproducible results and requires less than 9.5 min per sample for quantitation. The optimum pH for chymotrypsin-like esterase activity was 7.7-8.3. The Km and Vmax values were, respectively 25 microM and 0.241 pmol/microg protein/h with the use of enzyme extract obtained from mouse kidney. The approximate molecular mass of this enzyme was estimated to be 67000 by gel filtration. Chymotrypsin-like esterase activity was strongly inhibited by N-tosyl-L-phenylalaline chloromethyl ketone. Among the mouse organs examined, the highest specific activity of the enzyme was found in lung. This new method would be useful for clarification of the physiological role of this enzyme.