Sample preparations How to calculate activity Units/mL=(21.84)(volofenzyme)(A50/min)(dilution)( 1.1) where: dilution is the dilution factor of enzyme or sample 1.1 refers to reaction volume in mL vol. of enzyme (= mitochondria sample) should be converted to mL 21.84=m between ferrocytochrome c and ferricytochrome c at 550nm.