[burningdesire]

X and Y have the following molar absorptivity in 0.1 mol L-1 NaOH :


Wavelength (nm)         molar absorptivity (L mol-1 cm-1)
               X            Y
   
295               2375            2375

280               1576                5225

The absorbance of a solution of a mixture of X and Y in 0.1 mol L-1 NaOH was 0.500 at 295nm and 0.700 at 280nm (in a 1cm cuvette)

a) What are the concentrations of X and Y in the mixture?   

b) A protein HAW2A contains 420 amino acids, including 7 X and 4 Y residues. Calculate the molar absorptivity of HAW2A in alkali at 280nm (assume that only these residues contribute to the absorbance at 280 nm).

c) What would be the approximate absorbance of a solution of 1 mg mL-1 of HAW2A at 280nm?
[Assume average Mr of an amino acid residue in a protein = 100]   



I'm not sure how to do part b and c?

Is it 7*1576+4*5225=ecl? If so what is the concentration (c)?

[burningdesire]

Can anyone help me at all?

[Borek]

Is it 7*1576+4*5225=ecl

You are more or less on the right track, but it is not about ecl (if I guess correctly what you mean). You are calculating specific molar absorptivity - just e. c & l don't matter.

[burningdesire]

Is it 7*1576+4*5225=ecl

You are more or less on the right track, but it is not about ecl (if I guess correctly what you mean). You are calculating specific molar absorptivity - just e. c & l don't matter.

What exactly do you mean? Please elaborate
I thought since only X and Y contribute to the absorbance, the total absorbance by the protein would be the 7*1576+4*5225... then ecl of the protein equals 7*1576+4*5225?

Thanks

[Borek]

Please elaborate - what is ecl?

[burningdesire]

Please elaborate - what is ecl?

sorry it's the beer lambert law
http://upload.wikimedia.org/math/9/b/0/9b0e5de0240230229685407660c47ba9.png

[Borek]

OK, what is the meaning of all three symbols - e, c and l?