(4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoyl-CoA + acetyl-CoA => 3-oxo-(6Z,9Z,12Z,15Z,18Z,21Z)-tetracosahexaenoyl-CoA + CoA
(4z,7z,10z,13z,16z,19z)-docosahexaenoyl-coa + acetyl-coa => 3-oxo-(6z,9z,12z,15z,18z,21z)-tetracosahexaenoyl-coa + coa