Abstract EN:

Myristic acid, the 14 carbon saturated fatty acid (C14:0), is present in small amounts in animal tissues (0. 5-4% of total fatty acids). However, it is abundant in milk fat (7-12 %). The cellular functions of myristic acid particularly through its protein acylation ability (called N-terminal myristoylation) are stillnot known. The past studies have focused on its ability to increase cholesterol concentration when it is present in excess in the diets. When provided at moderate levels, no evidence for deleterious affects of myristic acid has been reported (< 4 % of total energy). The goal of our work was therefore to characterize the myristoylation reaction and the effect of myristic acid, via or not myristoylation, on the biosynthesis of polynsatured fatty acids and sphingolipids. Our results show first that exists two isoforms of the N-myristoyltransferase (NMT1 and NMT2) in rats, as in other mammals. This enzyme catalyzes the formation of an amide bond between the N-terminal glycine of the protein and a myristoyl-CoA. The specific activity of NMT1 is about four times higher than NMT2 activity. In studies on the affinity of NMT1 have shown that it has several substrates in vivo, but its strongest activity is found with the C14:0. The enzyme is able to form in vitro an amide bond between a peptide that is substrate of myristoylation and the C12:0, C16:0 and C18:1 n-9. In vivo this ability is not found.