Monomeric human cathepsin E.

Cathepsin E is a homodimer, consisting of two monomers linked by an inter-molecular disulphide bond. The cysteine residue involved is located near to the N-terminus of the mature proteinase. By mutating this residue to alanine, a monomeric form of human cathepsin E was engineered and purified. The activity of the resultant enzyme was not altered significantly (in terms of its ability to hydrolyse two chromogenic peptide substrates; and its susceptibility to inhibition by pepstatin). However, the stability of the mutant enzyme to alkaline pH and to temperature was markedly reduced.