Influence of body size on the composition of lipids and fatty acids in mitochondria of the mussel Mytilus edulis Linnaeus

Mitochondria play a crucial role in energy metabolism, and the relationship between metabolic rate and body size (metabolic allometry) may be linked to membrane properties and their lipid composition. We studied the influence of body size on the lipid and fatty acid composition of mitochondria in bivalve mollusks, specifically in mussels Mytilus edulis L. from the White Sea. This study analyzed mussels of varying sizes, ranging from 0.3 to 12.7 g of soft tissue wet mass. Mitochondria were isolated from gill tissues, and their lipid and fatty acid composition was determined. It was shown that, unlike phospholipids and triacylglycerols, the sterol proportion in mitochondrial membranes varied depending on mussel size. Larger mussels had lower cholesterol proportion but higher levels of monounsaturated fatty acids. In the composition of mitochondrial phospholipids, saturated fatty acids (SFAs), especially palmitic (16:0) and stearic (18:0) acids, predominated. The proportion of SFAs decreased with increasing mussel size. Conversely, monounsaturated fatty acids (MUFAs) showed a positive correlation with body size, significantly increasing in larger individuals. The proportion of polyunsaturated fatty acids (PUFAs) in White Sea mussel mitochondria was relatively low (less than 25% of the total fatty acids) and did not depend on body mass. The reduced proportion of PUFAs is characteristic of bivalve mitochondria from Arctic seas and long-lived bivalve species. Our data indicate the relative stability of the lipid and fatty acid composition of White Sea mussel mitochondria. Such fatty acid profile of mitochondrial phospholipids is likely a biochemical adaptation, enabling mussels to maintain effective activity of membrane-associated proteins regardless of their body size.