Isotope discrimination is a common feature of biosynthesis in nature, with the result that different classes of @entity505 compounds frequently display different @entity7352 /(12)C ratios. The @entity7352 / @entity41202 ratio of lipid in @entity415 tuber tissue is considerably lower than that for starch or protein. We have collected respiratory @entity515 from @entity415 discs in successive periods through 24 hr from the time of cutting-an interval in which the respiration rate rises 3-5-fold. The @entity7352 / @entity41202 ratio of the evolved @entity515 was determined for each period, and compared with the @entity7352 /(12)C ratios of the major tissue metabolites. In the first hours the @entity505 isotope ratio of the @entity515 matches that of lipid. With time, the ratio approaches that typical of starch or protein. An estimation has been made of the contribution of lipid and @entity1735 to the total respiration at each juncture. In connection with additional observations, it was deduced that the basal, or initial, respiration represents lipid metabolism-possibly the alpha-oxidation of long chain @entity1718 -while the developed repiration represents conventional @entity6626 cycle oxidation of the products of @entity1735 glycolysis. The true isotopic composition of the respiratory @entity515 may be obscured by fractionation attending the refixation of @entity515 during respiration, and by @entity515 arising from dissolved @entity515 and @entity3157 preexisting in the tuber. Means are described for coping with both pitfalls.

The prevalence of @entity505 -13 in respiratory carbon dioxide as an indicator of the types of endogenous substrate. The change from lipid to @entity1735 during the respiratory rise in XXXX slices.

@entity7352 :: ('CHEBI:36928', 'Chemical') :: ['(13)C'] @entity1735 :: ('CHEBI:16646', 'Chemical') :: ['carbohydrate'] @entity41202 :: ('CHEBI:36931', 'Chemical') :: ['(12)C'] @entity515 :: ('CHEBI:29334', 'Chemical') :: ['CO(2)'] @entity3157 :: ('CHEBI:17544', 'Chemical') :: ['bicarbonate'] @entity415 :: ('4113', 'Species') :: ['potato'] @entity6626 :: ('CHEBI:27093', 'Chemical') :: ['tricarboxylic acid'] @entity505 :: ('MESH:D002244', 'Chemical') :: ['carbon'] @entity1718 :: ('MESH:D005227', 'Chemical') :: ['fatty acids']
@entity415 :: (4113,Species) :: ['potato']
