C-terminus

https://doi.org/10.1351/goldbook.09737
End of an amino acid chain (protein or polypeptide), terminated by a carboxylic group.
Source:
PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1154 (https://doi.org/10.1515/pac-2016-1120)