Fatty acid desaturase

A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond. These desaturases are classified as: 
In the biosynthesis of essential fatty acids, an elongase alternates with different desaturases (for example, Δ6desaturase) repeatedly inserting an ethyl group, then forming a double bond.
Function.
Maintain structure and function of membranes within cells of the organisms above. This is important when temperatures changes and the membrane is under distress. The enzyme creates the double bond C-Cs which allow the membrane to become more fluid and the temperature is decreased. When temperatures change, a phase transition occurs. In the case of a temperature decrease, the membrane gels and becomes solid which can result in cracks and the imbedded proteins cannot partake in conformational changes, therefore it is important to maintain membrane fluidity.
Role in human metabolism.
Fatty acid desaturase appear in all organisms: for example, bacteria fungus plants animals and humans. Four desaturases occur in humans: Δ9 desaturase, Δ6 desaturase, Δ5 desaturase, and Δ4 desaturase.
Δ9 desaturase, also known as stearoyl-CoA desaturase-1, is used to synthesize oleic acid, a monounsaturated, ubiquitous component of all cells in the human body. Δ9 desaturase produces oleic acid by desaturating stearic acid, a saturated fatty acid either synthesized in the body from palmitic acid or ingested directly.
Δ6 and Δ5 desaturases are required for the synthesis of highly unsaturated fatty acids such as eicosopentaenoic and docosahexaenoic acids (synthesized from α-linolenic acid); arachidonic acid and adrenic acid (synthesized from linoleic acid). This is a multi-stage process requiring successive actions by elongase and desaturase enzymes. The genes coding for Δ6 and Δ5 desaturase production have been located on human chromosome 11.
Vertebrates are unable to synthesize polyunsaturated fatty acids because they do not have the necessary fatty acid desaturases to "convert oleic acid (18:1"n"-9) into linoleic acid (18:2"n"-6) and α-linolenic acid (18:3"n"-3)". Linoleic acid and α-linolenic acid are essential for human health and development.
Human fatty acid desaturases include: DEGS1; DEGS2; FADS1; FADS2; FADS3; FADS6; SCD4; SCD5
Classification.
Δ-desaturases are represented by two distinct families which do not seem to be evolutionarily related.
Family 1 includes Stearoyl-CoA desaturase-1 (SCD) ().
Family 2 is composed of:
Acyl-CoA dehydrogenases.
Acyl-CoA dehydrogenases are enzymes that catalyze formation of a double bond between C2 (α) and C3 (β) of the acyl-CoA thioester substrates. Flavin adenine dinucleotide (FAD) is a required co-factor.