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 e 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 use Use Excel and matrices to set up the problem and solve for the concentrations of NAD+ and NADH. Do concentrations from the two procedures match?

Explanation / Answer

I am showing the basic method to solve this question.

A = e*l*c

At 260 nm, absorbance is due to both compounds

So, A = A1 + A2 = e1*l*c1 + e2*l*c2

1.25 = 18000*1*c1 + 14400*1*c2 ---(1)

At 340 nm, absorbance is due to NADH only

So, A = e2*l*c2

0.26 = 6220*1*c2 -----(2)

Solving (1) and (2) we get :

c2 = [NADH] = 4.18*10-5 M

c1 = [NAD+] = 3.6*10-5 M

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