Factors Affecting the Activity of Ascorbate Oxidase

Ascorbate oxidase is a copper-containing enzyme, located in the cytoplasm or combined with the cell wall, and coupled with other redox reactions to act as a terminal oxidase. It can catalyze the oxidation of ascorbic acid, has anti-aging effects, and plays an important role in material metabolism in plants. Under the catalysis of this enzyme, molecular oxygen can oxidize ascorbic acid to dehydroascorbic acid, which exists in the cytosol and cell wall, and the enzyme contains copper. Pyruvate, isocitrate, a. Ketoglutarate, malic acid, glucose, 6. Phosphoric acid, 6. Phosphogluconic acid can dehydrogenate protons under the action of dehydrogenase. The hydrogen protons are transferred to the coenzyme, and then the hydrogen protons are transferred to ascorbic acid through glutathione. Under the action of ascorbate oxidase, ascorbic acid is oxidatively dehydrogenated, and hydrogen combines with oxygen to form water. The following are some factors that affect the activity of ascorbate oxidase.

Temperature

Studies have shown that ascorbate oxidase has two peaks of activity when the temperature is below 45°C, and one peak when the temperature is above 50°C. Enzyme activity lasts up to 40 minutes when the temperature is below 50°C. And as the temperature rises, the activity peak will advance. When the temperature is above 55°C, the duration of enzyme activity is very short, only 20 minutes at 60°C.

pH value

The activity of ascorbate oxidase is greatly affected by pH. Studies have shown that ascorbate oxidase exhibits higher activity in the pH range of 5-7. The strongest activity is at pH 5, which can reach 1.06 activity units. As the pH value increases, the activity decreases and the greater the pH value, the greater the drop. When the pH is 9, the activity is only 0.35 active units. It can be seen that the optimal pH value for the action of ascorbate oxidase is 5.

Low temperature, ozone and decompression

Low temperature can keep the enzyme activity low and reduce the respiration rate of the fruit. O3 inhibits the activity of ascorbic acid oxidase. Tests have shown that the greater the O3 concentration between 0 and 500 mg/m³, the stronger the inhibitory effect. O3 has the effect of maintaining the content of ascorbic acid. The general trend between 0~500mg/m³ is that the higher the concentration of O3, the higher the content of ascorbic acid. Decompression has a significant effect on inhibiting the activity of ascorbate oxidase, maintaining fruit firmness and ascorbic acid content. The reason may be that the decompression makes this enzyme in a swelling state and hinders its binding to the substrate. Wet and cold storage and ordinary cold storage were carried out on winter jujube. Wet and cold storage can inhibit the vitamin C content and ascorbic acid oxidase activity of winter jujube, and improve the storage effect of winter jujube.

Plant growth regulator

Common plant growth regulators are Uniconazole (S3307), Gibberellin (GA3), Abscisic acid (ABA) and 2,4-Dichlorophenoxyacetic acid (2,4-D).

Among them, S3307 can increase the activity of ascorbate oxidase, and ABA treatment significantly promotes the increase of ascorbate oxidase activity. GA3 delays the increase of ascorbate oxidase. It is speculated that the effect of ABA in promoting fruit senescence is also reflected in the effect on enzyme activity. 2,4-D can promote the activity of ascorbate oxidase at a certain low concentration. When the concentration of 2,4-D is larger, the activity is partially inhibited. The energy metabolism is blocked, which interferes with the normal metabolic process of the plant body, and gradually weakens the metabolism. In severe cases, the metabolism stops, which leads to death. This is the harmful effect of high concentrations of 2,4-D on plants.

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