Involved in the initial and rate-limiting step of peroxisomal beta-oxidation of straight-chain saturated and unsaturated very-long-chain fatty acids (PubMed:7876265, PubMed:15060085, PubMed:17458872, PubMed:17603022, PubMed:32169171, PubMed:33234382). Catalyzes the desaturation of fatty acyl-CoAs such as palmitoyl-CoA (hexadecanoyl-CoA) to 2-trans-enoyl-CoAs ((2E)-enoyl-CoAs) such as (2E)-hexadecenoyl-CoA, and donates electrons directly to molecular oxygen (O(2)), thereby producing hydrogen peroxide (H(2)O(2)) (PubMed:7876265, PubMed:17458872, PubMed:17603022). Shows highest activity against medium-chain fatty acyl-CoAs. Shows optimum activity with a chain length of 10 carbons (decanoyl-CoA) in vitro. Is active against a much broader range of substrates and shows activity towards long-chain fatty acyl-CoAs. a 2,3-saturated acyl-CoA + O2 = a (2E)-enoyl-CoA + H2O2 a 2,3-saturated acyl-CoA + O2 = a (2E)-enoyl-CoA + H2O2 a 2,3-saturated acyl-CoA + O2 = a (2E)-enoyl-CoA + H2O2 hexadecanoyl-CoA + O2 = (2E)-hexadecenoyl-CoA + H2O2 hexadecanoyl-CoA + O2 = (2E)-hexadecenoyl-CoA + H2O2 dodecanoyl-CoA + O2 = (2E)-dodecenoyl-CoA + H2O2 dodecanoyl-CoA + O2 = (2E)-dodecenoyl-CoA + H2O2 O2 + octanoyl-CoA = (2E)-octenoyl-CoA + H2O2 O2 + octanoyl-CoA = (2E)-octenoyl-CoA + H2O2 decanoyl-CoA + O2 = (2E)-decenoyl-CoA + H2O2 decanoyl-CoA + O2 = (2E)-decenoyl-CoA + H2O2 O2 + tetradecanoyl-CoA = (2E)-tetradecenoyl-CoA + H2O2 hexadecanedioyl-CoA + O2 = (2E)-hexadecenedioyl-CoA + H2O2 hexadecanedioyl-CoA + O2 = (2E)-hexadecenedioyl-CoA + H2O2 (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA + O2 = (2E,5Z,8Z,11Z,14Z,17Z)-icosahexaenoyl-CoA + H2O2 (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA + O2 = (2E,5Z,8Z,11Z,14Z,17Z)-icosahexaenoyl-CoA + H2O2 O2 + tetracosanoyl-CoA = (2E)-tetracosenoyl-CoA + H2O2 glutaryl-CoA + O2 = (2E)-glutaconyl-CoA + H2O2 hexanoyl-CoA + O2 = (2E)-hexenoyl-CoA + H2O2 O2 + octadecanoyl-CoA = (2E)-octadecenoyl-CoA + H2O2 (6Z,9Z,12Z,15Z,18Z,21Z)-tetracosahexaenoyl-CoA + O2 = (2E,6Z,9Z,12Z,15Z,18Z,21Z)-tetracosaheptaenoyl-CoA + H2O2 Optimum pH is 8.5. Optimum temperature at pH 7.5 is 40 degrees Celsius with no activity at 50 degrees Celsius. Optimum pH is 7.5-8.5. Optimum temperature at pH 7.5 is 47.5 degrees Celsius with 57% activity retained at 50 degrees Celsius. Lipid metabolism; peroxisomal fatty acid beta-oxidation. Homodimer (PubMed:32169171). Interacts with LONP2 (PubMed:18281296). Widely expressed with highest levels of isoform 1 and isoform 2 detected in testis. Isoform 1 is expressed at higher levels than isoform 2 in liver and kidney while isoform 2 levels are higher in brain, lung, muscle, white adipose tissue and testis. Levels are almost equal in heart. The disease is caused by variants affecting the gene represented in this entry. The gene represented in this entry is involved in disease pathogenesis. Isoform 1 and isoform 2 can reverse the Acox1 null phenotype in mouse which is characterized by severe microvesicular hepatic steatosis, sustained activation of PPARA, spontaneous massive peroxisome proliferation and eventual development of hepatocellular carcinomas. Isoform 2 is more effective in reversal of the phenotype than isoform 1 (PubMed:20195242). Belongs to the acyl-CoA oxidase family. Extended N-terminus.