NCC MALONYLTRANSFERASE CATALYZES THE FINAL STEP OF CHLOROPHYLL BREAKDOWN IN RAPE (BRASSICA-NAPUS)

Of the three final products of chlorophyll breakdown that in senescing cotyledons of oilseed rape are accumulated progressively, the nonfluo rescent Bn-NCC-1 is the most abundant catabolite. It represents the ma lonylester of the minor catabolite Bn-NCC-3. The in vitro malonylation of Bn-NCC-3 into Bn-NCC-1 was investigated. Extracts from senescent a s well as from presenescent cotyledons contained corresponding activit ies in the presence of malonyl-coenzyme A as the co-substrate. Malonyl transferase activity exhibited pH- and activation optima at 8 and 34 d egrees, respectively, and it was saturable with an apparent Michaelis constant of 58 mu M for Bn-NCC-3. The partially purified enzyme recogn ized chlorophyll catabolites as substrate specifically, provided that they had a free hydroxyl group in the ethyl side chain of pyrrole B. ( C) 1998 Elsevier Science Ltd. All rights reserved