In biochemistry, NAD(P)+ transhydrogenase (Si-specific) (EC 1.6.1.1) is an enzyme that catalyzes the chemical reaction Thus, the two substrates of this enzyme are NADPH and NAD+, whereas its two products are NADP+ and NADH.
Si-specific transhydrogenase is a soluble protein found in some Gammaproteobacteria and gram-positive bacteria.
[1] Its chief function in vivo is the reoxidization of excess NADPH.
[2] This enzyme belongs to the family of oxidoreductases, specifically those acting on NADH or NADPH with NAD+ or NADP+ as acceptor.
The systematic name of this enzyme is NADPH:NAD+ oxidoreductase (Si-specific).