[stride23]

I used UNIPORT to find information on the human aconitase (mitochondrial) enzyme which gives the extinction coefficients:

Extinction coefficients:

Extinction coefficients are in units of  M-1 cm-1, at 280 nm measured in water.

Ext. coefficient    84520
Abs 0.1% (=1 g/l)   0.989, assuming all pairs of Cys residues form cystines


Ext. coefficient    83770
Abs 0.1% (=1 g/l)   0.981, assuming all Cys residues are reduced


You will notice that under “extinction coefficients”, there are two values given,
depending on whether the cys residues exist as reduced cysteine, or as half-cystine. This reflects
a trace absorbance of 280 nm light by cystine. Assume that the cysteines are reduced, and using
the appropriate extinction coefficient, calculate the protein concentration (in mg/ml) of a solution
of pure human mitochondrial aconitase with an absorbance at 280 nm of 0.6 AU (measured in a
cell with a 1 cm pathlength).
Also calculate the concentration of the protein in units of moles/l (i.e. M). You may want
to express that concentration in mM or μM.

I'm having trouble of finding the concentration due to the two extinction coefficients given. Which one do I use? Upon doing this question, the concentration in the beer-lambert law A=ecl shows that 'c' is in units of mol/L. How can I convert that to mg/ml?

[Babcock_Hall]

The problem itself tells you which extinction coefficient to use.  In general how does one calculate a mass from an amount in moles?