FAD3

FAD3, or fatty acid desaturase 3, is an enzyme that introduces a double bond at the delta-15 (Δ15) position of fatty acids in the endoplasmic reticulum of plant cells. Its primary substrate is linoleic acid (18:2), which it desaturates to produce alpha-linolenic acid (18:3), an essential omega-3 fatty acid.

FAD3 belongs to the fatty acid desaturase (FAD) family and is typically ER-localized. It functions in contrast to plastid-localized delta-15 desaturases such as FAD7 and FAD8. In many plants, FAD2, another ER desaturase, acts first to convert oleic acid (18:1) to linoleic acid (18:2); FAD3 then converts 18:2 to 18:3, contributing to the composition of seed oils and membrane lipids.

Biochemical characteristics include being an integral membrane protein that requires molecular oxygen and electrons supplied by a cytochrome b5–dependent system. A non-heme iron center at the active site is involved in the desaturation reaction.

Biological and agricultural relevance centers on alpha-linolenic acid as a plant-derived omega-3 fatty acid and a precursor for longer-chain omega-3 lipids. Variation in FAD3 expression influences seed oil composition and nutritional quality. Biotechnological approaches targeting FAD3 have been used to increase ALA content in crops such as soybean and canola, aiming to enhance the nutritional value of edible oils.

See also: fatty acid desaturase (FAD) family; FAD2; FAD7; FAD8; alpha-linolenic acid.