NADH disodium salt, trihydrate, reduced: β-NADH, a pyridine nucleotide and biologically active form of nicotinic acid, is a coenzyme necessary for the catalytic reaction of certain enzymes.
β-NAD+ is a carrier for hydride ion, forming β-NADH. The hydride ion is enzymatically removed from a substrate molecule by the action of dehydrogenases such as, malic dehydrogenase and lactic dehydrogenase.
These enzymes catalyze the reversible transfer of a hydride ion from malate or lactate to β-NAD+, forming the reduced product, β-NADH. Unlike β-NAD+ which has no absorbance at 340 nm, β-NADH absorbs at 340 nm.
The increase in absorbance (with the formation of β-NADH) or the decrease in absorbance (with the formation β-NAD+) is the basis for measurement of activity of many enzymes at 340 nm. Many metabolites and enzymes of biological interest are present in tissues at low concentrations.
With the use of β-NADH as a cofactor and several enzymes in a multistep system, known as enzyme cycling, much greater sensitivity for detection of these components is achieved. β-NADH is fluorescent whereas β-NAD+ is not.
This difference in fluorescence provides a sensitive fluorescent measurement of the oxidized or reduced pyridine nucleotides at concentrations down to 10- M. Discussion of optimizing the fluorescence intensity and identification of interfering substances has been reported. β-NADH should be stored desiccated and protected from light.