Human Liver Mitochondria: Relation of a Particular Lipid Composition to the Mobility of Spin‐Labelled Lipids

Abstract

Human liver mitochondria contain twice as much lipid as those from the rat. This increased lipid content is not associated with an increase in content of a particular lipid class; human liver mitochondria contain higher amounts (compared to the rat) of each of the lipid classes. There are differences in fatty acid composition of total lipids and phospholipids between human and rat liver mitochondria. The differences are related to the essential fatty acids: human liver mitochondria contain more linoleic acid and less arachidonic acid than those of the rat; such a pattern of distribution of fatty acids in liver mitochondria has not been reported for any other species. The unsaturation of lipids is lower in human than in rat liver mitochondria as judged by the unsaturation index and the ratio of unsaturated to saturated fatty acids. Spin‐labelled fatty acids were used to probe the fluidity of membrane lipids in human and rat liver mitochondria. A greater mobility of spin label motion was noticed in the human case, a discontinuity of the electron spin resonance parameter as a function of temperature was noticed at a lower temperature for human than for rat. The higher fluidity of human membrane might arise from a lesser immobilization of lipids by proteins in comparison with the rat liver membranes. Copyright © 1978, Wiley Blackwell. All rights reserved