The Fixation of C14O2 into Tartaric and Malic Acids of Excised Grape Leaves.

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Abstract
C14O2 was fixed into malic, citric, tartaric, and some unidentified organic acids by excised grape leaves (Vitis vinifera). Fixation into malic acid occurred both in the light and in the dark but into (+)- tartaric acid only in the light. The highest specific activity of the tartaric acid was only about 1/1000 the value for malic acid and was obtained when 3 hours of light with C14O2 was followed by a 21-hour dark period in the absence of C14O2. After a continous light treatment of 24 hours in the presence of C14O2, the tartaric acid had a lower specific activity. In the shortest light experiment, 3 hours, the internal carbons of tartaric acid were more highly labeled (75%) than the carboxyl carbons (25%), but when followed by a dark period or a continuous light treatment, the molecule became uniformly labeled. In contrast, in the short light experiment, the carboxyl carbons of malic acid were more highly labeled (85%) than the internal carbons (15%), becoming more uniformly labeled with longer treatment in the light or when a dark period followed the light. In the dark, only the carboxyl carbons of malic acid were labeled. Enzyme preparations from grape leaves were similar to extracts from other leaves in that only (-)- and meso-tartrate were active in the diphos-phopyridine nucleotide-dependent tartaric dehydrogenase system.