Microderivatization of 4-[18O]hydroxyproline and quantitation with a benchtop mass spectrometer

Analysis of 4-hydroxyproline using 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol derivatization and micellar electrokinetic chromatography combined with laser-induced fluorescence detection

Micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) detection was used for internal standard (pyrrolidinol) based quantification of 4-hydroxyproline (Hyp) in muscle hydrolysates. Hydrolysates were first derivatized with o-phthaldialdehyde to reduce primary amine interference and then 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol (NBD) to enable selective detection of secondary amines. This method allows for rapid and sensitive detection of hydroxyproline in dilute hydrolysates using commercially available capillary electrophoresis equipment.

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Micellar electrokinetic chromatography of hydroxyproline and other secondary amino acids in biological samples with laser-induced fluorescence detection

Micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) was used for the rapid and sensitive detection of hydroxyproline in serum and hydrolyzed urine that were pre-column derivatized with 9-fluorenylmethyl chloroformate (FMOC). The application of the combined o-phthalaldehyde (OPA)/FMOC derivatization in MEKC for the selective detection of secondary amino acids in biological samples is investigated.

Determination of free and total proline and hydroxyproline in plasma and tissue samples by gas chromatography with flame photometric detection

A selective and sensitive method for the determination of free and total proline (Pro) and 4-hydroxyproline (Hyp) by gas chromatography (GC) was developed. For free Pro and Hyp analysis, plasma and tissue homogenate were extracted with methanol. For total Pro and Hyp analysis, these samples were hydrolysed in 6 M HCl. After removal of primary amino compounds by the reaction with o-phthaldialdehyde, Pro and Hyp in methanol extract and acid hydrolysate were converted into their N-dimethylthiophosphoryl methyl ester derivatives and then determined by GC with flame photometric detection using a DB-5 capillary column. This method was successfully applied to small samples without prior clean-up, and Pro and Hyp in these samples could be analysed without any influence from coexisting substances. Overall recoveries of Pro and Hyp added to plasma and tissue samples were 92-106%. The analytical results of free and total Pro and Hyp in human plasma and mouse tissue samples are presented.

Laser-induced fluorescence detection of 9-fluorenylmethyl chloroformate derivatized amino acids in capillary electrophoresis

Laser-induced fluorescence (LIF) was applied to the detection of 9-fluorenylmethyl chloroformate (FMOC-Cl) derivatized amino acids separated by capillary electrophoresis. Fluorescence excitation was provided by a pulsed, KrF laser operating at 248 nm. A limit of detection of 5 x 10(-10) M was obtained for FMOC-alanine (S/N = 2). Separation of FMOC-derivatized proline, hydroxyproline, and sarcosine was achieved with a 20 mM borate buffer (pH 9.2), and the separation of FMOC-derivatized amino acid standard mixture was obtained using a 20 mM borate buffer (pH 9.2) containing 25 mM sodium dodecyl sulfate.

Gas chromatography-mass spectrometry determination of 18O2 in 18O-labelled 4-hydroxyproline for measurement of collagen synthesis and intracellular degradation

The use of gas chromatography-mass spectrometry (GC-MS) and 18O2, a stable isotope which is incorporated into collagen during the post-translational conversion of proline to hydroxyproline, offers the potential advantages of high levels of sensitivity and specificity as compared to other techniques for measuring rates of collagen synthesis and degradation in vitro and vivo. Trifluoracetylation and methanol esterification of hydroxyproline yields two derivatives of hydroxyproline: N,O-trifluoroacetyl methyl 4-hydroxy-L-proline (N,O-TFA-Hyp) and N-trifluoroacetyl methyl 4-hydroxy-L-proline (N-TFA-Hyp). In the past, N-TFA-Hyp, which yields the 16O/18O-containing m/z 182/184 ion pair [M-COOH3]+ when analyzed by electron impact ionization GC-MS, has been proposed for analysis of 18O-enriched collagen. Although N,O-TFA-Hyp can be converted to N-TFA-Hyp by solvolysis, we find that this leads to degradation of the chromatography in GC-MS and demonstrate here that this extra chemical step is unnecessary if the m/z 278/280 ion pair (representing the [M-COOCH3]+. fragment) is measured by selected ion monitoring. By labelling fibroblasts in culture with 18O2, a sample of isotope-enriched collagen was obtained which was used to calibrate the GC-MS over the range 0.5-49% atom percent enrichment (APE). The greater sensitivity of 18O2 versus [15N]proline for labelling newly synthesized collagen was demonstrated by the finding of a ten-fold higher enrichment in the former isotope when administered to cell cultures at the same precursor APE. Thus, the approach described herein permits the determination of total hydroxyproline and APE on the same sample avoiding additional processing steps while maintaining the quality of chromatography and the sensitivity of detection. Measurement of absolute rates of both collagen synthesis and intracellular degradation of newly synthesized collagen in cell cultures is thus possible. Preliminary results comparing collagen metabolism in pairs of fibroblasts from hypertrophic scars and normal skin in post-burn patients are presented.