What is the difference between NADH and NADH2? Can they be used interchangeably during ETS?
They are often used interchangeably to indicate the reduced form of NAD+NADX+. The overall reaction when oxidizing some molecule RH2RHX2 is: RH2+NAD+⟶NADH+H++RRHX2+NADX+⟶NADH+HX++R. The proper reduced NAD+NADX+ is NADHNADH (it accepts two electrons and one proton), but sometimes NADH2NADHX2 is used to account for that second hydrogen that gets removed from the substrate being oxidized. The notation NADH2NADHX2 doesn't really take into account the fact that the second hydrogen is charged, and not bound to the NADNAD in the same way that the first hydrogen is, so it is confusing. The notation: "NADH+H+NADH+HX+" is more correct and is also sometimes used....