Detailed introduction about the ascorbate oxidase

 

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Detailed introduction about the ascorbate oxidase

Basic Information

Ascorbate oxidase is a copper-containing enzyme located in the cytoplasm or bound to the cell wall. It is coupled with other redox reactions to act as a terminal oxidase, catalyzes the oxidation of ascorbic acid, and has anti-aging effects in plants. It has an important role in the metabolism of matter. Under the catalysis of this enzyme, molecular oxygen can oxidize ascorbic acid to dehydroascorbic acid, which is present in the cytosol and cell walls, and contains copper in the enzyme. Pyruvic acid, isocitric acid, a. Ketoglutaric acid, malic acid, glucose, 6. Phosphoric acid, 6. Phosphogluconate can remove H protons under the action of dehydrogenase, transfer H protons to coenzyme, and then transfer H protons to ascorbic acid via glutathione. Ascorbic acid is oxidized by ascorbate oxidase. H, H combines with oxygen to form water.

 

Factors affecting ascorbate oxidase activity

 

Temperature

Studies have shown that ascorbate oxidase has two peaks of activity at temperatures below 45 °C, peaks above 50 °C, and enzyme activity lasts for 40 min at temperatures below 50 °C, and with increasing temperature High, the activity peak will be advanced, when the temperature is above 55 °C, the enzyme activity lasts for a short time, only 20min at 60 °C.

 

PH value

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

 

Light intensity and nitrogen form

Under the different light and nitrogen treatment conditions of tomato growth process, it was found that the growth of plants supplying ammonium nitrogen was inhibited under high light intensity, the chlorophyll content of fresh leaf unit was significantly decreased, and the ascorbate oxidase was significantly higher than the supply of nitrate. Nitrogen plants, and in low light conditions, there is no significant difference in nitrogen morphology. In the process of tobacco growth, similar treatments were obtained in the different treatments of nitrate nitrogen and ammonium nitrogen. As the amount of ammonium nitrogen increased, the ascorbic acid content increased, indicating that ascorbate oxidase activity was low.

 

Radiation

The seeds of Chinese cabbage were irradiated with different doses of 60Co γ-rays. It was found that changes in the ascorbate oxidase zymogram in the seedlings could increase the germination rate and emergence rate, stimulate seedling growth, accelerate development and increase yield, but there was instability of radiation stimulation. The problem of "reproducible" is poor. After low-dose γ-irradiation of cabbage seeds, the ascorbate oxidase activity of seedlings increased, which may be the reason for the low dose to promote plant resistance and stimulate growth and development.

 

Low temperature, ozone and decompression

Low temperature can keep the enzyme activity low, reduce the respiration rate of the fruit, and O3 inhibits the activity of ascorbate oxidase. The test proves that the greater the concentration of O3 between 0 and 500 mg/m3, the stronger the inhibition. O3 has the effect of maintaining ascorbic acid content. The overall trend between 0 and 500 mg/m3 is that the higher the O3 concentration, the higher the ascorbic acid content. Decompression has a significant effect on inhibiting ascorbate oxidase activity, maintaining fruit firmness and ascorbic acid content, which may be caused by decompression to cause the enzyme to expand and hinder binding to the substrate. The winter jujube is treated by wet storage and ordinary cold storage. The wet and cold storage can inhibit the vitamin C content and ascorbate 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. ABA treatment significantly promoted the activity of ascorbate oxidase, GA3 delayed the increase of ascorbate oxidase, and speculated that ABA promoted fruit senescence also showed the effect on enzyme activity. 4-D can promote ascorbate oxidase activity at a certain low concentration; when the concentration of 2,4-D is large, the activity is partially inhibited, energy metabolism is blocked, and the normal metabolic process of the plant is disturbed, so that metabolism Gradually weakened, in severe cases, metabolism stops, leading to death, which is the damage of high concentration of 2,4-D on plants.

 

Other information

1 commonly used method for determination of ascorbate oxidase activity

The enzyme activity is expressed by an enzyme unit (the amount of enzyme which oxidizes 1 g of reducing ascorbic acid in an enzyme unit of 1 min), that is, an enzyme unit/g fresh weight. The commonly used measurement method is the iodometric method, which is a classic method. The instrument used is simple and accurate. The second is spectrophotometry. This method has high sensitivity and accuracy, good reproducibility, wide application and good selectivity. The third is the oxygen electrode analysis method, which has high sensitivity and good accuracy, but the oxygen electrode is very sensitive to temperature changes, and the temperature needs to be kept constant during the measurement; the fourth is pulse polarography, which is simple in operation and good in reproducibility. Consistent with the results of the iodometric method.

Ascorbate oxidase exhibits higher activity in the pH range of 5-7, and is most active at pH 5.

Ascorbic acid oxidase has two peaks of activity at temperatures below 45 ° C, and a peak occurs above 50 ° C. The temperature is at

When the temperature is below 50 °C, the enzyme activity lasts for 40 min, and the activity peak will advance with the increase of temperature. When the temperature is above 55 °C, the enzyme activity lasts for a short time, only 20 min at 60 °C.

 

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