Calculating fraction of protein unfolded from spectroscopy data
I've plotted the data for ease of answering, though it is not necessary if you know what to look for in the data.



As expected, the melting curves are sigmoidal with horizontal asymptotes at approximately 0.5 and 1. You should be able to see this in the raw data as well: the absorbances hover around 0.5 before rising rapidly and then plateauing around 1.

You want the fraction of unfolded protein as a function of absorbance, so you need to normalize this data to the range of [0,1]. There's a straightforward formula for this which, put into the terms of your question, would be:

$f = \frac{A_{222} - min(A_{222})}{max(A_{222}) - min(A_{222})}$

$f = \frac{A_{222} - 0.5}{1 - 0.5}$

$f = \frac{A_{222} - 0.5}{0.5} = 2(A_{222} - 0.5)$

Intuitively, you might think about it as follows: at low temperatures, when the protein is folded, absorbance is 0.5. Consider this a blank or baseline measurement which gives the absorbance of the solution when no protein is unfolded. Since you are only interested in the signal from unfolded protein, you can subtract this value (0.5) from the rest of the data.