Abstract
The changes of L-ascorbic acid (ASA) content during storage in fruits and vegetables depends on interaction between ascorbate oxidase (E.C. 1.10.3.3) and peroxidase (E.C. 1.11.1.7) which oxidize ASA and oxidized ascorbate reductase (E.C. 1.6.5.4) which reduces oxidized ascorbate. The object of this experiment is to determine characteristics of oxidized ascorbate reductase and differences of this enzyme's activities in several fruits and vegetables. We also investigated the changes of the activities during development of chilling injury (browning) and yellowing that a decrease of ASA content was remarkable.
The results obtained were as follows:
1. This enzyme catalyzed the reduction of L-monodehydroascorbic acid (MDHA) by means of NADH as a coenzyme and showed high activity in tris-HCl buffer.
2. The optimum pH and temperature of this enzyme were about 7.5-8.0 and 35 °C, respectively.
3. This enzyme was extremely sensitive to SH reagents such as p-hydroxy mercuribenzoate (PHMB), 5, 5'-dithio-bis-(2-nitrobenzoic acid) (DTNB), and monoiodoacetic acid and inhibited by chlorogenic acid. It was also inhibited by AgNO3 (1×10-3M, 1×10-4M) and FeCl2 (1×10-3M), but other metal ions didn't actually exert on its activity.
4. The activities of this enzyme were high in pumpkin, cucumber, and carrot in which ascorbate oxidase activities were high, while in leaf vegetables, potatoes, and sweet potatoes its activities were low.
5. This enzyme's activities during development of chilling injury in sweet pepper seeds and sweet potatoes in which ASA content decreased remarkably increased temporarily before occurrence of chilling injury and then declined with the advance of chilling injury.
6. The activity of this enzyme in spinach leaves lowered with the decrease of ASA content with yellowing.
