AN ESSENTIAL LYSINE RESIDUE OF GREEN CRAB (SCYLLA-SERRATA) ALKALINE-PHOSPHATASE

The values of pK(a) (10.38) and H-ion (10.92 Kcal/mol) have been deter mined for the ionizing groups controlling activity of green crab alkal ine phosphatase. The results suggest that -NH2 of lysine residue respo nsible for the ionization with pK(c) = 10.38 and Delta H degrees (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-trinitrobenzenesu lfonic acid leads to complete inactivation. The two results coincide w ith each other. Quantitative assessment of the data indicates that amo ng the reactive -NH2 groups modified only one is essential for the act ivity of the enzyme.