ACC Oxidase

ACC (1-aminocyclopropane-1-carboxylic acid) is an important intermediate in the biosynthesis of ethylene, a plant hormone that plays a crucial role in various physiological and developmental processes. The conversion of ACC to ethylene is catalyzed by ACC oxidase, also known as ethylene-forming enzyme (EFE).

Function of ACC Oxidase

ACC oxidase is an enzyme that catalyzes the final step in the biosynthesis of ethylene. It oxidizes ACC, releasing ethylene gas as a byproduct. This enzyme is found in the endoplasmic reticulum of plant cells and is tightly regulated to control the levels of ethylene produced by the plant.

Mechanism of Action

The catalytic mechanism of ACC oxidase involves the oxidation of the α-amino group of ACC to form ethylene. It requires molecular oxygen as a co-substrate and uses ascorbic acid as a cofactor. This reaction involves the following steps:

1. Binding: ACC oxidase binds to ACC, positioning it for catalysis.
2. Oxidation: Molecular oxygen is introduced into the active site of ACC oxidase, where it reacts with the α-amino group of ACC.
3. Decarboxylation: The oxidized ACC undergoes decarboxylation, resulting in the release of ethylene and cyanide as byproducts.
4. Regeneration: The enzyme is regenerated and can bind to another molecule of ACC to continue the catalytic cycle.

Regulation of ACC Oxidase

ACC oxidase is subject to tight regulation to ensure proper control of ethylene production in plants. Its activity can be regulated at multiple levels, including transcriptional, post-transcriptional, and post-translational regulation. Factors such as hormones, developmental cues, and environmental stimuli can influence ACC oxidase activity.

Conclusion

ACC oxidase plays a crucial role in ethylene biosynthesis by catalyzing the conversion of ACC to ethylene. Understanding the mechanism and regulation of ACC oxidase is essential for unraveling the complex signaling pathways and physiological responses mediated by ethylene in plants.