This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is (S)-carnitine:NAD+ oxidoreductase.
Setyahadi S, Ueyama T, Arimoto T, Mori N, Kitamoto Y (1997). "Purification and properties of a new enzyme, D-carnitine dehydrogenase, from Agrobacterium sp. 525a". Biosci. Biotechnol. Biochem. 61 (6): 1055–8. doi:10.1271/bbb.61.1055. PMID9214773.