Analysis of dipeptides in urine by gas chromatography/mass spectrometry: implications for collagen breakdown in iminodipeptiduria following a study of the dipeptides by electron impact and chemical ionization.

Dipeptides in the urine of a patient suffering from dermatological purpura, associated with iminodipeptiduria , were determined by gas chromatography/mass spectrometry. The dipeptides were identified as R-proline and R'-hydroxyproline where R is any one of the residues, glycyl, alanyl, valyl, leucyl, isoleucyl, seryl, aspartyl, glutamyl, prolyl, phenylalanyl and R' is alanyl, valyl, leucyl or isoleucyl, seryl, prolyl, glutamyl, phenylalanyl. The predominance of proline- and hydroxyproline-containing dipeptides and the percentage distributions of the other amino acid residues, R and R', strongly implicate an abnormality of collagen metabolism. Structural assignments are confidently based on (a) gas chromatographic retention times, (b) electron impact mass spectra and automatic comparison with reference to spectra stored in a specialized library, (c) chemical ionization mass spectra with isobutane and methanol as reactant gases and (d) the use of deuteriated acetic anhydride as a derivatizing agent.