Specific activities and keratin/casein ratios of the purified wild-type and mutant SAPB enzymes using keratin and casein as substrates.

aSpecific activity is defined as units (U) of activity per amount (mg) of protein. 1 U of protease activity was defined as the amount of enzyme that liberated 1 µg tyrosine per min under the optimal temperature and pH values of the respective recombinant enzymes using keratin or casein as a substrate. Proteins were estimated by the Bradford method using the Dc protein assay kit obtained from Bio-Rad Laboratories (Inc., Hercules, CA, USA). bThe experiments were conducted three times and ± standard errors are reported. cThe relative activity is calculated by taking the specific activity of the wild-type as 1.00. Specific activities and keratin/casein ratios of the purified wild-type and mutant SAPB enzymes using keratin and casein as substrates.