Abstract
Contributions of omega-oxidation to overall fatty acid oxidation in slices from livers of ketotic alloxan diabetic rats and of fasted monkeys are estimated. Estimates are made from a comparison of the distribution of 14C in glucose formed by the slices from omega-14C-labeled compared to 2-14C-labeled fatty acids of even numbers of carbon atoms and from [1-14C]acetate compared to [2-14C]acetate. These estimates are based on the fact that 1) the dicarboxylic acid formed via omega-oxidation of a omega-14C-labeled fatty acid will yield [1-14C]acetate and [1-14C]succinate on subsequent beta-oxidation, if beta-oxidation is assumed to proceed to completion; 2) only [2-14C]acetate will be formed if the fatty acid is metabolized solely via beta-oxidation; and 3) 14C from [1-14C]acetate and [1-14C]succinate is incorporated into carbons 3 and 4 of glucose and 14C from [2-14C]acetate is incorporated into all six carbons of glucose. From the distributions found, the contribution of omega-oxidation to the initial oxidation of palmitate by liver slices is estimated to between 8% and 11%, and the oxidation of laurate between 17% and 21%. Distributions of 14C in glucose formed from 14C-labeled palmitate infused into fasted and diabetic rats do not permit quantitative estimation of the contribution of omega-oxidation to fatty acid oxidation in vivo. However, the distributions found also indicate that, of the fatty acid metabolized by the whole animal in the environment of glucose formation, at most, only a minor portion is initially oxidized via omega-oxidation. As such, omega-oxidation cannot contribute more than a small extent to the formation of glucose.
Highlights
Contributions of o-oxidation to overall fatty acid oxidation in slices from livers of ketotic alloxan diabetic rats and of fasted monkeys are estimated
Distributions of 14Cin the glucose units from the monkey liver glycogens are recorded in Table 1, along with the percentage of the added 14C recovered in COz, and in the glucose that was degraded following purification
The percent of the 14Cadded as 14C-labeled acetate that was recovered in 14C02ranged from 9.0 to 19.0% and in glucose from 2.8 to 10.1%
Summary
Sodium [l-14C]acetate, sodium [2-14C]acetate,and [l-14C]palmitic acid were purchased from New England Nuclear Corp., Boston, MA. [2-14C]Palmitic acid and [3-14C]palmiticacid were purchased from the Applied Science Laboratories, Inc., State College, PA. [10-14C]Palmiticacid, [16-14C]palmiticacid, and [12-14C]lauricacid were purchased from the Commission d’Energie Atomique, DCpartment des RadioClemknts, Gif-sur-Yvette, France. [10-14C]Palmiticacid, [16-14C]palmiticacid, and [12-14C]lauricacid were purchased from the Commission d’Energie Atomique, DCpartment des RadioClemknts, Gif-sur-Yvette, France. Sodium [l-14C]acetate, sodium [2-14C]acetate,and [l-14C]palmitic acid were purchased from New England Nuclear Corp., Boston, MA. [2-14C]Palmitic acid and [3-14C]palmiticacid were purchased from the Applied Science Laboratories, Inc., State College, PA. Their purity was established as previously described [15]
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