Oxygen fixation into hydroxyproline in etiolated maize seedlings : verification by tandem mass spectrometry.

Etiolated maize (Zea mays L.) seedlings were grown in the dark for 5 days in an atmosphere enriched with 10.0 atom% (18)O(2). Hydroxyproline was isolated from root and shoot tissues, purified, and methylated. It was not possible to determine (18)O incorporation into hydroxyproline by conventional mass spectrometry because the final product was not sufficiently pure. The final product was analyzed successfully by tandem mass spectrometry. The (18)O content of the hydroxyl oxygen atom was 10 +/- 0.7 atom%. This result demonstrates that the hydroxyl oxygen atom in hydroxyproline was derived exclusively from molecular oxygen.