Journal of Lipid Research, Vol 19, 591-600, Copyright © 1978 by Lipid Research, Inc.
Contribution of omega-oxidation to fatty acid oxidation by liver of rat and monkey
W Kam, K Kumaran and BR Landau
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.