Calculating Protein Concentration from Kilo Units (KU)
From the page linked from your link:


  Unit Definition
  
  One unit will convert 1.0 μmole of phospho(enol)pyruvate to pyruvate
  per min at pH 7.6 at 37 °C.


So, the unit is defined by activity, and there is no way to know how many molecules or milligrams of protein are included