Omega-3 desaturase catalyzes the conversion of arachidonic acid
(20:4) to eicosapentaenoic acid (20:5) by creating a double bond at
the third position from the methyl end of arachidonic acid.
Research has indicated that this enzyme converts 31% of arachidonic
acid to eicosapentaenoic acid and has greater activity on C20 and
C22 fatty acid substrates than on C18 substrates.