Category: catabolism
Lysine is essential (humans cannot synthesize) and the most-abundant basic amino acid. Catabolism goes via saccharopine pathway (LKR / SDH — bifunctional enzyme deficient in hyperlysinemia) → α-aminoadipate → α-ketoadipate → glutaryl-CoA → acetyl-CoA + CO2. Lysine is the precursor for CARNITINE biosynthesis (multi-step: lysine → trimethyllysine → β-hydroxy-trimethyllysine → 4-N-trimethylaminobutyraldehyde → γ-butyrobetaine → L-carnitine; the last step is hydroxylated by BBOX1, which is also a target of the ketogenic-mimetic mildronate / meldonium). Hyperlysinemia is generally benign; glutaric aciduria type 1 (GCDH deficiency, downstream) causes a macrocephalic neonatal encephalopathy.