β-Oxidation — activation, carnitine shuttle, one spiral (8 enzymes)
Long-chain fatty acids are activated in the cytosol, ferried into the matrix as acylcarnitine, then shortened by one acetyl-CoA per turn. This teaching set is one ACSL isoform, the CPT1A/CACT/CPT2 shuttle, and one MCAD–crotonase–HADH–T1 spiral — not every ACAD isozyme.
Long-chain acyl-CoA synthetase 1 ACSL1
FA + ATP + CoA → acyl-CoA + AMP + PPi
ANL two-half reaction. Mesh is T. thermophilus 1V26 — human ACSL1 has no PDB. Occupancy is AMP + myristate, not intact acyl-AMP.
EC 6.2.1.3 · PDB 1V26
▶ OPEN SIMULATORCarnitine palmitoyltransferase 1A CPT1A
palmitoyl-CoA + carnitine → palmitoylcarnitine + CoA
Outer-membrane gate. Mesh is human CRAT 1NM8 — CPT1A catalytic domain has no PDB. Malonyl-CoA inhibition is named, not this pocket.
EC 2.3.1.21 · PDB 1NM8
▶ OPEN SIMULATORCarnitine/acylcarnitine translocase CACT · SLC25A20
acylcarnitine (IMS) ⇌ acylcarnitine (matrix)
Carrier, not an EC enzyme. Mesh is bovine ANT 1OKC — human CACT has no PDB. ANT ≠ CACT. CATR is a named inhibitor, not substrate.
SLC25A20 · PDB 1OKC
▶ OPEN SIMULATORCarnitine palmitoyltransferase 2 CPT2
palmitoylcarnitine + CoA → palmitoyl-CoA + carnitine
Inner-membrane reverse of CPT1A. Mesh is rat CPT2 2RCU — human CPT2 has no PDB. Occupancy is an amide analog (BUJ), not the physiological ester.
EC 2.3.1.21 · PDB 2RCU
▶ OPEN SIMULATORMedium-chain acyl-CoA dehydrogenase ACADM · MCAD
octanoyl-CoA + ETFox → (2E)-octenoyl-CoA
FAD-linked dehydrogenation on 8SGP. Occupancy is FAD, not octanoyl-CoA. Acyl overlay is pig 3MDE. Not VLCAD / SCAD.
EC 1.3.8.7 · PDB 8SGP
▶ OPEN SIMULATORShort-chain enoyl-CoA hydratase ECHS1 · crotonase
(2E)-butenoyl-CoA + H₂O → (3S)-3-hydroxybutanoyl-CoA
Hydration on apo 8ZRU. Crotonyl-CoA is rebuilt from an 8ZRX CAA overlay — CAA is acetoacetyl-CoA, not the enoyl substrate.
EC 4.2.1.17 · PDB 8ZRU
▶ OPEN SIMULATORShort-chain 3-hydroxyacyl-CoA DH HADH
(3S)-3-hydroxybutanoyl-CoA + NAD⁺ → acetoacetyl-CoA + NADH
NAD-linked oxidation on 1F0Y. Occupancy is NAD⁺ + the oxo product CAA, not the 3-hydroxy substrate. Opposite stereo from BDH1; different gene.
EC 1.1.1.35 · PDB 1F0Y
▶ OPEN SIMULATORMitochondrial 3-ketoacyl-CoA thiolase ACAA2 · T1
acetoacetyl-CoA + CoA → 2 acetyl-CoA
Thiolysis on 4C2J. Occupancy is free CoA, not 3-ketoacyl-CoA. Cys92 is CSO on this crystal. Not ACAT1 (T2, ketogenesis).
EC 2.3.1.16 · PDB 4C2J
▶ OPEN SIMULATOR