Question: mention the chemical change that proinsulin undergo to be able to act as mature insulin
[{'answer': 'post translational modification', 'provenance': [{'wikipedia_id': '249971', 'title': 'Proinsulin', 'start_paragraph_id': 9, 'start_character': 4, 'end_paragraph_id': 9, 'end_character': 35, 'bleu_score': 1.0, 'section': 'Section::::Synthesis and Post-translational Modification.\n'}]}, {'provenance': [{'wikipedia_id': '249971', 'title': 'Proinsulin', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 585, 'bleu_score': 0.9796927878356411, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5872295079286616542}, 'section': 'Section::::Synthesis and Post-translational Modification.\n'}]}, {'provenance': [{'wikipedia_id': '249971', 'title': 'Proinsulin', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5872295079286616542}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '249971', 'title': 'Proinsulin', 'start_paragraph_id': 9, 'start_character': 0, 'end_paragraph_id': 9, 'end_character': 562, 'bleu_score': 0.9013170106978211, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5872295079286616542}, 'section': 'Section::::Synthesis and Post-translational Modification.\n'}]}, {'provenance': [{'wikipedia_id': '249971', 'title': 'Proinsulin', 'section': 'Section::::Synthesis and Post-translational Modification.\n', 'start_paragraph_id': 9, 'end_paragraph_id': 9, 'meta': {'evidence_span': ['The post translational modification', 'The post translational modification of proinsulin to mature insulin only occurs in the beta cells of the islets of Langerhans.', 'The post translational modification of proinsulin to mature insulin only occurs in the beta cells of the islets of Langerhans. When proinsulin is transported through the Golgi apparatus the C-peptide is cleaved.']}}]}]