L-Carnitine

Quaternary amine that shuttles fatty acids into mitochondria for energy production.

L-Carnitine isn't a peptide — it's the molecular "ferry" that carries fatty acids across the mitochondrial membrane so they can actually be burned for fuel. Without enough of it, fat can't reach the furnace. Used (injected, for far better uptake than oral) to support fat oxidation, exercise endurance, and recovery; the acetyl form (ALCAR) also crosses into the brain for a cognitive and energy effect. A simple, well-established metabolic helper rather than an exotic peptide.