Peptide analysis as amino alcohols by gas chromatography-mass spectrometry. Application to hyperoligopeptiduria. Detection of Gly-3Hyp-4Hyp and Gly-Pro-4Hyp-Gly.

A method for the qualitative analysis of oligopeptides in human urine in cases of peptiduria is described. After sample precleaning on a strongly acidic ion exchanger, the trifluoroacetyl/methyl esters were formed and the peptide derivatives were transformed into trifluoroethyl oligoamino alcohols according to Nau and Biemann. It was found that oligoamino alcohols could be isolated selectively on a weakly acidic ion exchanger. The O-trimethylsilylated trifluoroethyl oligoamino alcohols were separated on a SE-30 glass capillary column and analyzed by computer-assisted gas chromatography-mass spectrometry. In order to increase specificity and to facilitate mass spectrometric interpretation, aliquots of the sample were reduced separately with lithium-aluminium deuteride and hydride. Each peptide gave a pair of derivatives with characteristic mass differences of the ions, namely 2 mass units per reduced oxo group (deuterium-hydrogen-labelling of oxo groups by reduction). Correct identification is assumed only if both mass spectral patterns fit the theory. Sample volumes of 5--100 ml of urine are needed. About six samples can be derivatized per week. Three cases with suspected peptiduria were investigated and the following peptides were found: Gly-Pro-4Hyp-Gly; Gly-Pro-4Hyp; Gly-Hyp-Hyp (postulated isomer Gly-3Hyp-4Hyp); Pro-4Hyp and Gly-Pro. With exception of the tetrapeptide, these compounds could be detected also in the urine of a healthy child.