Patent ID: 7371553

Claim:
A method for assaying a chemically modified mutant enzyme to determine the degree of removal of a protein stain from a material, wherein said enzyme is a modified subtilisin enzyme comprising a subtilisin wherein an amino acid residue selected from the group consisting of residue 62, residue 96, residue 104, residue 107, residue 156, residue 166, residue 189, residue 209, residue 217, and residue 222 is replaced by a cysteine residue, wherein the cysteine residue is modified by replacing the thiol hydrogen in said cysteine residue with a substituent group providing a thiol side chain comprising a multiply charged moiety, and wherein said amino acid residue is numbered according to its equivalent in the amino acid sequence of Bacillus amyloliguefaciens subtilisin BPN′ (SEQ ID NO:2), said method comprising: a. applying said chemically modified mutant enzyme to a swatch of material comprising a piece of material and a protein stain fixed to said material; b. incubating the swatch; c. washing the incubated swatch; and d. determining the degree of removal of the protein stain from the material.