Cloning, expression, and nutritional regulation of the mammalian Delta-6 desaturase

Arachidonic acid (20:4(n-6)) and docosahexaenoic acid (22:6(n-3)) have a va riety of physiological functions that include being the major component of membrane phospholipid in brain and retina, substrates for eicosanoid produc tion, and regulators of nuclear transcription factors. The rate-limiting st ep in the production of 20:4(n-6) and 22:6(n-3) is the desaturation of 18:2 (n-6) and 18:3(n-3) by Delta-6 desaturase, In this report, we describe the cloning, characterization, and expression of a mammalian Delta-6 desaturase , The open reading frames for mouse and human Delta-6 desaturase each encod e a 444-amino acid peptide, and the two peptides share an 87% amino acid ho mology. The amino acid sequence predicts that the peptide contains two memb rane-spanning domains as well as a cytochrome b(5)-like domain that is char acteristic of nonmammalian Delta-6 desaturases. Expression of the open read ing frame in rat hepatocytes and Chinese hamster ovary cells instilled in t hese cells the ability to convert 18:2(n-6) and 18:3(n-3) to their respecti ve products, 18:3(n-6) and 18:4(n-3), When mice were fed a diet containing 10% fat, hepatic enzymatic activity and mRNA abundance for hepatic Delta-6 desaturase in mice fed corn oil were 70 and 50% lower than in mice fed trio lein, Finally, Northern analysis revealed that the brain contained an amoun t of Delta-6 desaturase mRNA that was several times greater than that found in other tissues including the liver, lung, heart, and skeletal muscle. Th e RNA abundance data indicate that prior conclusions regarding the low leve l of Delta-6 desaturase expression in nonhepatic tissues may need to be ree valuated.