The present invention relates to a process for the preparation of 5-norbornene-2-carboxylic acid from 5-norbornene-2-endo-carbonitrile and/or 5-norbornene-2-exo-carbonitrile. The invention relates in particular to a process which enables 5-norbornene-2-carboxylic acid to be prepared at a high substrate concentration. The invention furthermore relates to a polypeptide suitable for enzymatic conversion of 5-norbornene-2-carbonitrile to give 5-norbornene-2-carboxylic acid, in particular also with a high substrate concentration, and to a nucleic acid encoding said polypeptide, to a composition comprising 5-norbornene-2-carbonitrile to 5-norbornene-2-endo-carboxylic acid and 5-norbornene-2-exo-carboxylic acid, and to the use of said polypeptide.