Catalysis of the reaction: (9Z,12Z)-octadecadienoyl-CoA + 2 Fe(II)-[cytochrome b5] + 2 H+ + O2 = (6Z,9Z,12Z)-octadecatrienoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O. Can also use a substrate with 3 double bonds (a (9Z,12Z,15Z)-octadecatrienoyl-CoA and add a fourth double bond (a (6Z,9Z,12Z,15Z)-octadecatetraenoyl-CoA).
Source:PMID:7212717,
RHEA:47140,
RHEA:47144,
PMID:12713571
Comment
Note that this function was formerly EC:1.14.99.25.