The function of ACOX3 (acyl-CoA oxidase 3, pristanoyl, Ensembl gene identifier ENSG00000087008) is as follows. Involved in peroxisomal beta-oxidation of branched-chain fatty acids (BCFAs). Catalyzes the initial and rate-limiting dehydrogenation step that removes two hydrogen molecules and introduces a trans double bond between the alpha and beta carbons of the acyl CoA molecules while generating hydrogen peroxide as a by-product (PubMed:29287774). Metabolizes multi-methyl-branched fatty acyl-CoA esters such as (2S)-pristanoyl-CoA, displaying redundancy with ACOX3 (PubMed:29287774). Can oxidize straight-chain mono- and dicarboxylyl fatty acyl-CoAs with lower efficiency (By similarity) (PubMed:29287774). {ECO:0000250|UniProtKB:Q63448, ECO:0000269|PubMed:29287774}. Oxidizes the CoA-esters of 2-methyl-branched fatty acids. .