Desaturases

Desaturases are enzymes that introduce double bonds into fatty acyl chains, converting saturated fatty acids into unsaturated ones. Most desaturases are membrane-bound, residing in organelles such as the endoplasmic reticulum or mitochondria, and they catalyze the removal of two hydrogen atoms to form a cis double bond. The reactions require molecular oxygen and reducing equivalents (NADH or NADPH) and involve an iron-containing active site, often coordinated by histidine-rich motifs and electrons shuttled via cytochrome b5 or related partners.

Desaturases are commonly classified by the position at which they create a double bond, using the delta (Δ) or omega (ω) system. Δ-desaturases introduce double bonds at defined internal positions from the carboxyl end (for example, Δ9 desaturase creates a double bond at carbon 9 in stearoyl-CoA). Omega desaturases introduce bonds toward the methyl end (for example, ω-3 and ω-6 desaturases). In animals, desaturases act sequentially on essential fatty acids to produce longer-chain polyunsaturated fatty acids (PUFAs). Humans cannot synthesize linoleic acid (LA, 18:2 Δ9,12) or alpha-linolenic acid (ALA, 18:3 Δ9,12,15) and rely on these as dietary precursors for junctions such as arachidonic acid (AA) and eicosapentaenoic acid (EPA).

In plants and microorganisms, desaturases contribute to the natural diversity of membrane lipids, influencing fluidity and function across temperature ranges and developmental stages. Regulation occurs at transcriptional and enzymatic levels and responds to diet, temperature, and hormonal signals.

Applications include metabolic engineering of crops and microbes to alter fatty acid composition for nutrition or industrial purposes. Dysregulation or deficiency of desaturase activity is linked to metabolic and inflammatory processes, highlighting their biological and biomedical relevance.