acyl-CoA desaturase activity palmitoyl-CoA 9-desaturase activity https://github.com/geneontology/go-ontology/issues/29820 molecular_function RHEA:36931 GO:0032896 palmitoyl-CoA delta9-desaturase activity Catalysis of the reaction: hexadecanoyl-CoA + 2 Fe(II)-[cytochrome b5] + O2 + 2 H(+) = (9Z)-hexadecenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O.