Aminotransferase Activity in Relation to Increase of Alanine and Glutamate Contents in Plum Fruit during Maturation and Storage

Abstract

Alanine and glutamate contents in plum fruits always increased during maturation and storage, and the increase was especially remarkable when deterioration of the fruit was progressing. Glutamate pyruvate transaminase (GPT), alanine dehydrogenase (ADH), aspartate-β-decarboxylase (ADC), glutamate dehydrogenase (GDH) and glutamate oxaloacetate transaminase (GOT) activities in 'Sordum' fruit were assayed to clarify the mechanism of alanine and glutamate accumulation. The fruit was stored at 20°C and 30°C. GOT and GPT activities in the fruit increased during ripening on the tree, and the increase was more notable in GOT activity. As GOT and GPT activities increased, rapid increase of glutamate and alanine occurred. The other enzyme activities did not change. During the storage at 20°C, GOT and GPT activities increased remarkably after 3 and 7 days, respectively. The increase of GOT activity was higher than that of GPT activity, and the former increased prior to the latter. Changes of glutamate and alanine contents nthe fruit coincided with those of GOT and GPT activities. Both of these enzyme activities and the contents of alanine and glutamate were less in the fruit stored at 30°C than those at 20°C. Pyruvate and glutamate, the substrates of GPT, and α-ketoglutarate and aspartate, the substrates of GOT, shoWed a tendency to increase in the fruit ripened on the tree. After harvest, however, pyruvate and α-ketoglutarate contents decreased at the beginning of storage at 20°C and 30°C. After that, those increased at 20°C, while at 30°C pyruvate content decreased and α-ketoglutarate content increased. Glutamate content increased during storage at both temperatures. Changes of aspartate content was not consistent during storage at 20°C, but remarkable increase was found at 30°C. From these results, it is assumed that the increase of glutamate and alanine in the fruit would be caused by the increase of GOT and GPT activities, respectively. The increase of GPT activity seems to be caused with accumulation of glutamate produced bGOT, which is activated prior to GPT.