preferred_name: a (4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoyl-containing glycerolipid + 2 Fe(III)-[cytochrome b5] + 2 H2O => a (7Z,10Z,13Z,16Z,19Z)-docosapentaenoyl-containing glycerolipid + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+)