Extinction coefficient - (May/07/2009 )

Hi friends... I have few queries to be solved...
1.How to calculate extinction coefficient for hemocyanin at 335nm?

For example:
hemocyanin concentration was calculated using an extinction coefficient (ΕmM1cm) of 17.26, calculated from (E1%1cm) = 2.83 (Nickerson & Van Holde 1971) on the basis of a functional subunit of 74 000 (Antonini & Brunori 1974).

2.If we have extinction coefficient, How to calculate molar concentration?
3.How consistant is this quantificaiton of biochemical compounds based on extinction coefficient?
I am unacquainted to this UV spectroscopy, please explain with funtamental concepts.
Thank you for reading my query

1.How to calculate extinction coefficient for hemocyanin at 335nm?
The extinction coefficient is a measured value and can't be calculated.

2.If we have extinction coefficient, How to calculate molar concentration?
E=^mM/cm
measured extinction value divided by extinction coefficient gives mmol compound

3.How consistant is this quantificaiton of biochemical compounds based on extinction coefficient?
The extinctioncoefficient is a constant, this means the consistancy of the quantification depends on the error in the measurement itself

Dear Mr, Gerard,

Thank you very much for your prompt reply.
The following lines i've just copied from a Scientific paper, in this i could not understand E17.26 from 2.83...

"hemocyanin concentration was calculated using an extinction coefficient (Ε^mM_1cm) of 17.26, calculated from (E^1%_1cm) = 2.83 (Nickerson & Van Holde 1971) on the basis of a functional subunit of 74 000 (Antonini & Brunori 1974)."

I dont understand it either.

I would calculate is as follows

1%=10g/1000ml=10/74000*1000 mmol/l=0.135mmol/l
E^(0.135mM)_1cm = 2.83

E^(1mmol)_1cm = 2.83*(1/0.135)=21.0

May be the %extinction coefficient 2.83 is wrong. Instead it would have been 2.33, if so, the answer is 17.2. By formula 2.83 gives 21.0. you are right.