Catalysis of the reaction: (8Z,11Z,14Z)-eicosatrienoyl-CoA + 2 Fe(II)- + 2 H+ + O2 = (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + 2 Fe(III)- + 2 H2O. Can also use a substrate with 3 double bonds (a (8Z,11Z,14Z,17Z)-eicosatetraenoyl-CoA) and add a fourth double bond (a (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA).
acyl-CoA (8-3)-desaturase