(4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoate + reduced [NADPH--hemoprotein reductase] + O2 = 21-hydroxy-(4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoate + oxidized [NADPH--hemoprotein reductase] + H2O + H(+)
(4z,7z,10z,13z,16z,19z)-docosahexaenoate + reduced [nadph--hemoprotein reductase] + o2 = 21-hydroxy-(4z,7z,10z,13z,16z,19z)-docosahexaenoate + oxidized [nadph--hemoprotein reductase] + h2o + h(+)