Role of Oxygen Fixation in Hydroxyproline Biosynthesis by Etiolated Seedlings

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Abstract
Etiolated maize and soybean seedlings were grown for several days in atmospheres enriched with O18. Hydroxyproline subsequently isolated from the seedlings by column and thin-layer chromatography was labeled with excess O18, but proline was not. Control experiments in which seedlings were grown in H2O18 and unlabeled atmospheres demonstrated that neither proline nor hydroxyproline was labeled with excess O18. It was concluded that oxygen fixation is an essential feature of hydroxyproline biosynthesis in these seedlings, and that the hydroxyl oxygen atom in hydroxyproline is derived from molecular oxygen and not from water; similar results have been reported previously for sycamore cell suspensions.