Formation and breakdown of citric acid in Garcinia fruit. (Xanthochymus guttiferae).

Two hypotheses have been put forward to explain the large accumulation of organic acids in fruits: (a) organic acids are not formed in the fruit, but are translocated from the leaves to the fruits which would act merely as storage organs (1, 2) ; and (b) the presence of the organic acids in fruits is due to the conversion of carbohydrates to organic acids in the fruit vesicles and not to translocation from leaves (3, 4). Recent studies in this laboratory have shown the presence in the tissues of Citrus acida of the enzyme system concerned with synthesis of citric acid (5) and suggested that organic acids may generally be formed in the fruit itself. To investigate this question further, the levels of several enzymes likely to be involved in the formation and breakdown were studied in the fruit tissues of Garcinia (Xanthochymus guttijerae) at different stages of growth. An attempt was also made to purify three of these enzymes, namely, condensing enzyme, oxaloacetic carboxylase, and citric desmolase. The data on the partial purification of the condensing enzyme have already been reported (6) and those on the purification of the other two enzymes are reported in this paper. The results show that citric acid is formed from carbohydrate in Garcinia fruit tissue and suggest that its initial accumulation and subsequent disappearance are related to the changes in the activity of the condensing enzyme and other enzymes of the citric acid cycle.