The present Invention relates to new nitrilases with modified Substrate acceptance, the method to obtain them and the use of the aforesaid nitrilases. Said nitrilases are encoded by a polypeptide sequence, which at a Position corresponding to Position 296 in wild-type Alcaligenes faecalis comprises an amino acid which is not tyrosine. The Invention further relates to nucleic acid sequences and amino acid sequences encoding Said nitrilases, expression constructs comprising Said nucleic acid sequences, vectors comprising the nucleic acid sequences or the exPression constructs, to organisms, preferably microorganisms, comprising the nucleic acid sequences, expression constructs or vectors. The Invention additionally relates to a method for preparing carboxylic acids, preferably substituted chiral carboxylic acids from racemic nitriles.