text: An essential lysine residue of green crab (Scylla Serrata) alkaline phosphatase.
  The values of pKa (10.38) and Hion (10.92 Kcal/mol) have been determined for the ionizing groups controlling activity of green crab alkaline phosphatase. The results suggest that -NH2 of lysine residue responsible for the ionization with pKc = 10.38 and delta H(o)ion = 10.92 Kcal/mol is in the active site of the enzyme. Modification of lysine residues of the enzyme by an excess of 2,4,6-trinitrobenzenesulfonic acid leads to complete inactivation. The two results coincide with each other. Quantitative assessment of the data indicates that among the reactive -NH2 groups modified only one is essential for the activity of the enzyme.