NADH solution decays on its own? - (Jul/17/2007 )

I am working on the kinetic assay of an enzyme catalytic reaction. The reaction rate is monitored by continuous recording of NADH decay at 340 nm by using a UV spectrophotometer. I've just found out that the absorption of NADH solution decays with no substrates and enzymes added. Anyone has seen this before? Is the NADH spoiled or is the UV spectrophotometer down? Thanks

Hey
I am also monitoring NADPH absorbance derease at 340nm in myassay and I have seen That even on keeping in ice by the time i set up my control assay (where absorbance should not decrease) in 50 mins the absorbance of NADPH falls! So to achieve comparable data i jst make fresh NADPH. I also make it in acidified water pH around 3. I think u should set up appropriate controls for your assay and aalso definitelu use fresh NAPH.

Good luck