diff --git a/propka/group.py b/propka/group.py
index 3410c22..b03ef39 100644
--- a/propka/group.py
+++ b/propka/group.py
@@ -3,6 +3,11 @@ Data structures for groups
 ==========================
 
 Routines and classes for storing groups important to PROPKA calculations.
+
+
+.. versionchanged:: 3.4.0
+   Removed :func:`initialize_atom_group` as reading PROPKA inputs is no longer
+   supported.
 """
 import math
 import propka.ligand
@@ -1390,15 +1395,3 @@ def is_ion_group(parameters, atom):
     if atom.res_name.strip() in parameters.ions.keys():
         return IonGroup(atom)
     return None
-
-def initialize_atom_group(atom):
-    """Initialize an atom group.
-
-    Args:
-        atom:  atom to initialize
-    """
-        # try to initialise the group
-    group_attr = globals()[atom.group_label]
-    atom.group = group_attr(atom)
-    atom.group.model_pka = atom.group_model_pka
-    atom.group.model_pka_set = atom.group_model_pka_set
diff --git a/propka/input.py b/propka/input.py
index d77ef20..ff40a5e 100644
--- a/propka/input.py
+++ b/propka/input.py
@@ -14,7 +14,6 @@ from pkg_resources import resource_filename
 from propka.lib import protein_precheck
 from propka.atom import Atom
 from propka.conformation_container import ConformationContainer
-from propka.group import initialize_atom_group
 
 
 def open_file_for_reading(input_file):