Is likely involved in the aerobic desaturation system responsible for the synthesis of oleic acid from stearoyl-CoA; oleic acid is a precursor of mycobacterial membrane phospholipids and triglycerides. Catalyzes the conversion of stearoyl-CoA to oleoyl-CoA by introduction of a cis double bond between carbons 9 and 10 of the acyl chain. Requires the electron transfer partner Rv3230c to pass two electrons from NADPH to its active site diiron center. Is also able to catalyze the 9-desaturation of palmitoyl-CoA to palmitoleoyl-CoA. H(+) + NADPH + O2 + octadecanoyl-CoA = (9Z)-octadecenoyl-CoA + 2 H2O + NADP(+) Expected to bind 2 Fe(2+) ions per subunit. Inhibited by the anti-tuberculosis drug isoxyl (ISO). Lipid metabolism; fatty acid metabolism. Interacts with the electron transfer protein Rv3230c to form a functional acyl-CoA desaturase complex. Is expressed during the exponential growth. Is rapidly degraded by a mycobacterial protein degradation system that specifically targets the residues LAA at the C-terminus, leading to a post-translational proteolytic regulation of DesA3 essential activity. Strains lacking this gene are shown to be attenuated in a mouse tuberculosis model. Was identified as a high-confidence drug target. Belongs to the fatty acid desaturase type 1 family.