diff --git a/rpg/core.py b/rpg/core.py
index 3fa60554c48bc092fa37092ce8fa4539e502d3f7..046d6b9bbda9a5ae43502e56c05a1f3bf079b2b9 100644
--- a/rpg/core.py
+++ b/rpg/core.py
@@ -63,15 +63,26 @@ AA_MASS_AVERAGE = {"*" : 0.0,
 WATER_MASS = 18.01528
 """Mass of a water molecule."""
 
-AA_PKA = {"Nterm" : 8.0,
-          "C" : 8.3,
-          "D" : 4.1,
-          "E" : 4.1,
-          "H" : 6.0,
-          "K" : 10.8,
-          "R" : 12.5,
-          "Y" : 10.9,
-          "Cterm" : 3.1}
+# Biochemistry Stryer 7th
+#AA_PKA = {"Nterm" : 8.0,
+#          "C" : 8.3,
+#          "D" : 4.1,
+#          "E" : 4.1,
+#          "H" : 6.0,
+#          "K" : 10.8,
+#          "R" : 12.5,
+#          "Y" : 10.9,
+#          "Cterm" : 3.1}
+# IPC_peptide
+AA_PKA = {"Nterm" : 9.564,
+          "C" : 8.297,
+          "D" : 3.887,
+          "E" : 4.317,
+          "H" : 6.018,
+          "K" : 10.517,
+          "R" : 12.503,
+          "Y" : 10.071,
+          "Cterm" : 2.383}
 """pKa of important amino acid to compute pI."""
 
 def handle_errors(message="", err=1, error_type=""):