Recombinant Enterokinase (rEK) is the catalytic subunit of bovine enterokinase, which is expressed by the yeast Pichia pastoris and purified to yield a high enzyme activity preparation. rEK recognizes the sequence Asp-Asp-Asp-Asp-Lys and cleaves the peptide bond after the lysine residue. The enzyme can be used to cleave any fusion protein that carries this sequence.