Catabolism of porphobilinogen by etiolated barley leaves.

When [2,4-(14)C]porphobilinogen (PBG) or [2 (aminomethyl),5-(14)C]PBG is administered to etiolated barley (Hordeum vulgare L. var. Larker) leaves in darkness, label becomes incorporated into CO(2), organic and amino acids, sugars, lipids, and proteins during a 4-hour incubation. Less than 1% of the label, however, is incorporated into porphyrins. The rate of (14)CO(2) evolution from leaves fed [2,4-(14)C]PBG is strongly inhibited by anaerobiosis but is unaffected by aminooxyacetic acid, while the rate of (14)CO(2) evolution from [2(aminomethyl),5-(14)C]PBG is strongly inhibited by aminooxyacetic acid but is not affected by anaerobiosis.THESE RESULTS SUGGEST THAT: (a) exogenous PBG is taken up and metabolized by etiolated barley leaves; (b) PBG is not metabolized exclusively to porphyrins but can be converted to a variety of intermediary metabolites; (c) this metabolism involves reactions which are partially dependent upon O(2) and pyridoxal phosphate.