diff --git a/etfl/core/enzyme.py b/etfl/core/enzyme.py
index 6eaad36..56ffc88 100644
--- a/etfl/core/enzyme.py
+++ b/etfl/core/enzyme.py
@@ -115,7 +115,8 @@ def peptide(self, value):
     @property
     def molecular_weight(self):
         if not self._molecular_weight_override:
-            return molecular_weight(self.peptide, seq_type='protein') / 1000 # g.mol^-1 -> kg.mol^-1 (SI) = g.mmol^-1
+            # return molecular_weight(self.peptide, seq_type='protein') / 1000 # g.mol^-1 -> kg.mol^-1 (SI) = g.mmol^-1
+           return molecular_weight(str(self.peptide), 'protein') /1000
         else:
             return self._molecular_weight_override
 
diff --git a/etfl/core/rna.py b/etfl/core/rna.py
index 83c920c..8599a09 100644
--- a/etfl/core/rna.py
+++ b/etfl/core/rna.py
@@ -52,7 +52,8 @@ def init_variable(self, queue=False):
     @property
     def molecular_weight(self):
         if not self._molecular_weight_override:
-            return molecular_weight(self.rna, seq_type='RNA') / 1000 # g.mol^-1 ->
+           return molecular_weight(str(self.rna), seq_type='RNA') / 1000 # g.mol^-1 ->
+            # return molecular_weight(self.rna, seq_type='RNA') / 1000 # g.mol^-1 ->
             # kg.mol^-1 (SI) =
             # g.mmol^-1
         else:
@@ -125,4 +126,4 @@ def aminoacid(self):
 
     @property
     def molecular_weight(self):
-        return 25 # an average weight based on https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Sizes_and_Molecular_Weights_2pgs.pdf
\ No newline at end of file
+        return 25 # an average weight based on https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Sizes_and_Molecular_Weights_2pgs.pdf