CALCULATION OF SPECIFIC ENZYME ACTIVITY

I AM WORKING ON ANTIOXIDANT ANALYSIS
I WOULD LIKE TO KNOW HOW TO CALCULATE THE SPECIFIC ENZYME ACTIVITY OF SUPEROXIDE DISMUTASE BY MARKLUND METHOD.Can any body plz give the formula and the references.
if it is said that the assay mmixture should contain 0.2 mM PYROGALLOL then how do we make the stock?
thanking in advance