Disappearance of porphobilinogen deaminase activity in leaves before the onset of senescence.

The activity of porphobilinogen deaminase was measured in young and senescent or mature leaves of pepper (Capsicum annuum), and poinsettia (Euphorbia pulcherrima). Whereas high activity was found in the crude extracts of the young leaves, almost no activity was found in the extracts of senescent or mature leaves. The decrease in deaminase activity was not due to the presence of an isolatable inhibitor. By purifying the crude enzyme extracts from leaves of different ages on DEAE-cellulose columns it was shown that the decrease in deaminase activity was due to a real decrease in the amount of enzyme. Fruiting also decreased porphobilinogen deaminase activity. Several kinetic constants of the C. annuum deaminase were determined.