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Zebrafish cpt2 is the Danio rerio ortholog of human CPT2 (~70.9% sequence
homology) and encodes a mitochondrial carnitine O-palmitoyltransferase 2 that
reconverts long-chain acylcarnitines to acyl-CoA at the inner mitochondrial
membrane as part of the carnitine shuttle, enabling long-chain fatty acid
beta-oxidation.
"Independent zebrafish experimental work explicitly targets zebrafish **cpt2** as the ortholog of human CPT2 and reports **~70.9% sequence homology** between zebrafish cpt2 and human CPT2, supporting that “cpt2” in zebrafish refers to the same conserved enzyme class as the UniProt record."
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The core biochemical role of CPT2 is to reconvert fatty acylcarnitines to fatty
acyl-CoA at/near the inner mitochondrial membrane, releasing free carnitine for
recycling; CPT1 makes acylcarnitine, CACT transports it, and CPT2 uncouples it
back to acyl-CoA + L-carnitine for matrix beta-oxidation.
"**CPT2’s core biochemical role** is to **reconvert fatty acylcarnitines to fatty acyl-CoA** at/near the **inner mitochondrial membrane**, releasing free carnitine for recycling. A recent review describes the sequential steps: CPT1 converts fatty acyl-CoA to acylcarnitine, CACT transports it, and **CPT2 “uncouples” it back to fatty acyl-CoA + L-carnitine at the inner mitochondrial membrane**, enabling entry into β-oxidation."
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CPT2 is catalytically active on mid-length and long-chain acyl-CoA esters (C8-C18)
with virtually no activity on short-chain or ultralong-chain substrates,
consistent with its canonical role in long-chain fatty acid oxidation.
"A 2024 review summarizes that CPT2 is catalytically active on **mid-length and long-chain acyl-CoA esters**, but “virtually no activity” is observed on **short-chain** and **ultralong-chain** acyl-CoAs (and some non-fatty-acyl substrates), which is consistent with CPT2’s canonical role in LCFA oxidation rather than short-chain metabolism."
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In zebrafish, CPT2 protein was detected by Western blot in mitochondrial fractions
from larvae, providing direct evidence that the cpt2 gene product localizes to
mitochondria.
"In zebrafish specifically, CPT2 protein was experimentally detected by Western blot in **mitochondrial fractions** isolated from larvae, providing direct evidence that the zebrafish cpt2 gene product localizes to mitochondria (consistent with mitochondrial targeting signals in CPT2 proteins)."
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Morpholino knockdown of zebrafish cpt2 caused significant accumulation of
long-chain fatty-acylcarnitines, the expected metabolic consequence of a block at
the CPT2 step (impaired reconversion of acylcarnitines to acyl-CoA for
beta-oxidation).
"LC-MS/MS profiling demonstrated significant increases in long-chain fatty-acylcarnitines in knockdown larvae. Total acylcarnitines increased by approximately **~70% (translation-blocking; p<0.001)** and **~42% (splice-blocking; p≤0.05)** versus wild-type, consistent with a block at the CPT2 step (i.e., impaired reconversion of acylcarnitines to acyl-CoA for β-oxidation)."