TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation: (I) is prepared by providing a modified subtilisin with at least one amino acid residue at positions 62, 217, 222, 156 or 166, replaced with cysteine residues and replacing the thiol hydrogen of the cysteine with the substituent group providing a thiol side chain. Preferred Enzyme: The enzyme is protease, preferably Bacillus lentus subtilisin, where the amino acid replaced with cysteine is asparagine, leucine, methionine or serine. The amino acid replaced with a cysteine is in a subsite of the enzyme, such as S1, S1' and S2. In the thiol side chain R1 is 1-10C alkyl and is R2 is positively charged or negatively charged, NH3+ or SO3-. The modified amino acid is M222, L217, S156, S166 or N62. Preferably the modified amino acid is N62, where the thiol side chain is -SR1R2 and R1 is CH2CH2 and R2 SO3-. WIDER DISCLOSURE - Disclosed as new are modified enzymes comprising one or more residues replaced by cysteine residues. The cysteine residues are modified by replacing a thiol hydrogen with a substituent group providing a thiol side chain -SR6, where R6 is a C(1-6) alkyl, preferably, CH2C(CH3)3 or C5H11.    EXAMPLE - The gene for subtilisin from Bacillus lentus (SBL) was cloned into the bacteriophage M13mp19 vector for mutagenesis. The mutated sequences were cloned, excised and reintroduced into the expression plasmid GG274 in the B.subtilis host. The Cys-mutant M222C, B.lentus in buffer solution, was added to a solution of methyl methanethiosulfonate in 95% ethyl alcohol (EtOH). The modification was followed by activity measurements on 10 mul withdrawn samples. The reaction was terminated after 2.5 hours when addition of another aliquot of reagent to the reaction did not change the activity of the protease. The solution was purified on a desalting column. The protein was eluted and the specific activity of the modified mutant was found to be 64.3 U/mg as compared with the Cys mutant 47.1 U/mg. The wash performance of the modified enzyme was evaluated by measuring the removal of stain from EMPA 116 (blood/milk/carbon black on cotton) cloth swatches which had been pre-bleached. The pre-bleached EMPA 116 swatches were washed in detergent with 0.1 ppm enzyme for 20 minutes at 20 degrees Centigrade and were rinsed twice for 5 minutes in 1000 ml water. Swatches were dried and pressed, and the reflectance from the swatches was measured. Performance was reported as percent stain removal and percent stain removal relative to native B.lentus protease. The percent stain removal and percent relative stain removal of wild type SBL were 8.1 and 100, respectively and the modified mutant N62C-SCH2CH2SO3- had values of 13.4 and 165, respectively.