Lipid peroxidation forms ethylene from 1-aminocyclopropane-1-carboxylic acid and may operate in leaf senescence

Abstract

An enzyme system is described which oxidizes 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene under physiological conditions. It comprises linoleic acid, pyridoxal phosphate, manganese, and lipoxygenase (linoleate:oxygen oxidoreductase, EC 1.13.11.12). It requires oxygen and is specific for manganese; it can operate but only with greatly reduced yield in the absence of pyridoxal phosphate.An enzyme with the same properties was prepared from microsomal membranes of the seedling shoots of peas. Both have similar reactions to a variety of inhibitors and other reagents. The properties also resemble those of at least two of the in vivo systems recorded ih the literature. Intact green oat leaves also contain a similar system. Because there is a growing body of evidence that ethylene formation is associated with cell membranes and because the yields of ethylene from the complete system are much higher than those recorded for' other enzymes, it may be identical with the in vivo system acting in senescent leaves.

Dose-Response Relationships for N7-(2-Hydroxyethyl)Guanine Induced by Low-Dose [14C]Ethylene Oxide: Evidence for a Novel Mechanism of Endogenous Adduct Formation

“…This second reaction is inhibited by free radical scavengers (41) and can also occur nonenzymatically in the presence of pyridoxal phosphate, H 2 O 2 , and manganese or when a Cu(II)-ACC complex is incubated with H 2 O 2 alone (42,43). Of particular relevance to the current study is the fact that oxidation of linoleic acid by lipoxygenase in the presence of ACC generates ethylene (44). The mechanism is believed to involve generation of linoleic hydroperoxide, which is cleaved reductively to an alkoxy radical that reacts with ACC via hydride abstraction, affording an amine radical cation intermediate (45).…”

Authentic activity of the ethylene‐forming enzyme observed in membranes obtained from kiwifruit (Actinidia deliciosa)

“…A sensitivity to Co'-^ is sbared witb otber etbylenegei-ierating systems both in vivo (Yu & Yang, 1979) ana //( vitro (Konze & Kende, 1979;Bousquet &: Thiman, 1984). However, by contrast, in vitro systems pre\'iously described generally require Mn*" at //M concentrations (see Stegink & Siedow, 1986) ratber tban beirTg inhibited by Mn*".…”

“…This inhibitor completely prevented the generation of ethylene by a bomogenate of aetiolated pea shoots (Bousquet & Thiman, 1984) but the efl'ect of SHA.M on the in vivo EFE activity has not been widely investigated. Howe\-er tbe EEI<> activity of tissue discs of kiwifruit pericarp was found to be inhibited by 64 and 81 ",, by the addition of 0-1 and 1 mM SHAM, respectively, when assayed under the conditions described in Materials and Methods.…”

“…Activity ("") 68 + 5-7 80+1-9 51 +2-9 64 + 2-9 40 + 4-1 58 + 4-0 42 + 2-4 60 + 7-2 70 + 4-4 8-8+1-7 2-.S + ()-3 contrast other cell-free, ethylene-generating systems have been shown to be completely inhibited by EDl^A added in mM concentrations (Konze & Kende, 1979;Bousquet & Thiman, 1984;Stegink & Siedow, 1986).…”

“…The EEE of the kiwifruit membranes (Table 2) shares with cyanide-insensitive respiration (Schonbaum et al, 1971) and lipoxygenase (Parrish & Leopold, 1978;Bousquet & Thiman, 1984) a sensitivity to salicylhydroxamic acid (SHAM). This inhibitor completely prevented the generation of ethylene by a bomogenate of aetiolated pea shoots (Bousquet & Thiman, 1984) but the efl'ect of SHA.M on the in vivo EFE activity has not been widely investigated.…”