In enzymology, a 4-trimethylammoniobutyraldehyde dehydrogenase (EC 1.2.1.47) is an enzyme that catalyzes the chemical reaction

4-trimethylammoniobutanal + NAD⁺ + H₂O ${\displaystyle \rightleftharpoons }$ 4-trimethylammoniobutanoate + NADH + 2 H⁺

The 3 substrates of this enzyme are 4-trimethylammoniobutanal, NAD⁺, and H₂O, whereas its 3 products are 4-trimethylammoniobutanoate, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is 4-trimethylammoniobutanal:NAD+ 1-oxidoreductase. Other names in common use include 4-trimethylaminobutyraldehyde dehydrogenase, and 4-N-trimethylaminobutyraldehyde dehydrogenase. This enzyme participates in lysine degradation and carnitine biosynthesis.

• Carnitine biosynthesis
• γ-Butyrobetaine hydroxylase
• N^ε-Trimethyllysine hydroxylase

• Rebouche CJ, Engel AG (1980). "Tissue distribution of carnitine biosynthetic enzymes in man". Biochim. Biophys. Acta. 630 (1): 22–9. doi:10.1016/0304-4165(80)90133-6. PMID 6770910.