The compound nicotinamid adenine dinucleotide (NAD) is a biological molecule inv

Question

The compound nicotinamid adenine dinucleotide (NAD) is a biological molecule involved in a number of enzymatic reactions. It can exist in oxidized form (NAD+) and reduced form NADH. NAD+absorbs only at 260 nm with an epsilon value of 18000 M-1cm-1. NADH, on the other hand, absorbs at both 260 nm (epsilon@260 = 14400 M-1cm-1) and 340 nm (epsilon@340 = 6220 M- 1cm-1). A solution from a biological assay gives a total absorption of 1.25 at 260 nm and 0.26 at 340 nm. Assume a cuvette with a path length of 1 cm is used. Question: Repeat the process (both manually and Excel) by assuming that NAD_+ also absorbs at 340 with (epsilon @ 340 = 215 M - 1cm-1). Same total absorptions at the two wavelengths remain.

Explanation / Answer

Since there is no change in the Molar extinction coefficient values for NAD+ and NADH at 260nm, there is no change in the absorbance value at 260nm. It remains constant i.e 1.25.

If you assume that NAD+ also absorbs at 340 with Molar extinction coefficient value of 215M-1cm-1, total absorbance will become 0.51.

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