Glutamic Dehydrogenase and Glutamic-oxaloacetic Transaminase in Apple Tree Tissues.

A technique is described whereby active preparations of glutamic dehydrogenase (GDH) and glutamic-oxaloacetic transaminase (GOT) can be obtained from all apple tree tissues using a hand-operated coffee mill. The amount of insoluble polyvinylpyrrolidone required and the composition of the extractant have been investigated together with the degree of replication obtained and the stability of the resultant extracts. After extraction of all tissues the proportion of both GDH and GOT found in the supernatant was far greater than that in the mitochondria. Addition of calcium and some other metal ions to the assays resulted in some increase in GDH but had no effect on GOT activity. With crude extracts the effect of added calcium was small but after ultrafiltration or acid precipitation it was greatly increased. The co-factors NADH, NADPH and NAD were all active with GDH in extracts of apple leaves, stem bark and roots. No activity was found with NADP. In the presence of added calcium ions the ratios of activity NADH : NADPH and NADH : NAD were approximately 10:1 and 20:1 respectively. The seasonal variations in specific activity of GDH and GOT in apple leaves, stem bark and wood, and old and young roots were determined separately. The highest GDH activities were found in the leaves in October and in the stem bark in May, while in other tissues activities were generally higher in winter than in summer. The seasonal patterns for GOT activity were very similar to those for GDH except that in the leaves the level changed little through the year. The results are discussed in relation to published work on these enzymes in other plants and to their possible role in the apple tree. [ABSTRACT FROM AUTHOR]