Mitochondrial trifunctional enzyme catalyzes the last three of the four reactions of the mitochondrial beta-oxidation pathway (PubMed:8135828, PubMed:1550553, PubMed:29915090, PubMed:30850536). The mitochondrial beta-oxidation pathway is the major energy-producing process in tissues and is performed through four consecutive reactions breaking down fatty acids into acetyl-CoA (PubMed:29915090). Among the enzymes involved in this pathway, the trifunctional enzyme exhibits specificity for long-chain fatty acids (PubMed:30850536). Mitochondrial trifunctional enzyme is a heterotetrameric complex composed of two proteins, the trifunctional enzyme subunit alpha/HADHA described here carries the 2,3-enoyl-CoA hydratase and the 3-hydroxyacyl-CoA dehydrogenase activities while the trifunctional enzyme subunit beta/HADHB bears the 3-ketoacyl-CoA thiolase activity (PubMed:8135828, PubMed:29915090, PubMed:30850536). Independently of the subunit beta, the trifunctional enzyme subunit alpha/HADHA also has a monolysocardiolipin acyltransferase activity (PubMed:23152787). It acylates monolysocardiolipin into cardiolipin, a major mitochondrial membrane phospholipid which plays a key role in apoptosis and supports mitochondrial respiratory chain complexes in the generation of ATP (PubMed:23152787). Allows the acylation of monolysocardiolipin with different acyl-CoA substrates including oleoyl-CoA for which it displays the highest activity (PubMed:23152787). a (3S)-3-hydroxyacyl-CoA = a (2E)-enoyl-CoA + H2O a 4-saturated-(3S)-3-hydroxyacyl-CoA = a (3E)-enoyl-CoA + H2O (3S)-hydroxyoctanoyl-CoA = (2E)-octenoyl-CoA + H2O (3S)-3-hydroxydodecanoyl-CoA = (2E)-dodecenoyl-CoA + H2O (3S)-hydroxyhexadecanoyl-CoA = (2E)-hexadecenoyl-CoA + H2O a long-chain (3S)-3-hydroxy fatty acyl-CoA + NAD(+) = a long-chain 3-oxo-fatty acyl-CoA + H(+) + NADH (3S)-hydroxyoctanoyl-CoA + NAD(+) = 3-oxooctanoyl-CoA + H(+) + NADH (3S)-hydroxydecanoyl-CoA + NAD(+) = 3-oxodecanoyl-CoA + H(+) + NADH (3S)-3-hydroxydodecanoyl-CoA + NAD(+) = 3-oxododecanoyl-CoA + H(+) + NADH (3S)-hydroxytetradecanoyl-CoA + NAD(+) = 3-oxotetradecanoyl-CoA + H(+) + NADH (3S)-hydroxyhexadecanoyl-CoA + NAD(+) = 3-oxohexadecanoyl-CoA + H(+) + NADH 1'-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-3'-[1-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-glycerol + hexadecanoyl-CoA = 1'-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-3'-[1-(9Z,12Z-octadecadienoyl)-2-hexadecanoyl-sn-glycero-3-phospho]-glycerol + CoA (9Z)-octadecenoyl-CoA + 1'-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-3'-[1-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-glycerol = 1'-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-3'-[1-(9Z,12Z-octadecadienoyl)-2-(9Z-octadecenoyl)-sn-glycero-3-phospho]-glycerol + CoA (9Z,12Z)-octadecadienoyl-CoA + 1'-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-3'-[1-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-glycerol = 1',3'-bis-[1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phospho]-glycerol + CoA Lipid metabolism; fatty acid beta-oxidation. Heterotetramer of 2 alpha/HADHA and 2 beta/HADHB subunits; forms the mitochondrial trifunctional enzyme (PubMed:29915090, PubMed:30850536). Also purified as higher order heterooligomers including a 4 alpha/HADHA and 4 beta/HADHB heterooligomer which physiological significance remains unclear (PubMed:8163672, PubMed:29915090). The mitochondrial trifunctional enzyme interacts with MTLN (By similarity). Protein stability and association with mitochondrion inner membrane do not require HADHB. Up-regulated by thyroid hormone (at protein level). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. In the N-terminal section; belongs to the enoyl-CoA hydratase/isomerase family. In the central section; belongs to the 3-hydroxyacyl-CoA dehydrogenase family. Wrong choice of frame.