May play a key role in the regulation of the intracellular concentration of adenosylhomocysteine, which is a strong inhibitor of SAM-dependent methyltransferases. Catalyzes the hydrolysis of S-adenosyl-L-homocysteine into L-homocysteine and adenosine. H2O + S-adenosyl-L-homocysteine = adenosine + L-homocysteine Binds 1 NAD(+) per subunit. Amino-acid biosynthesis; L-homocysteine biosynthesis; L-homocysteine from S-adenosyl-L-homocysteine: step 1/1. Homotetramer; dimer of dimers. Each protomer consists of two large domains, the substrate-binding domain and the cofactor-binding domain, which are separated by a deep crevice forming the substrate-access channel to the active site, and a small C-terminal oligomerization domain. Belongs to the adenosylhomocysteinase family.