. 2014 Sep 29;9(9):e108367. doi: 10.1371/journal.pone.0108367

Table 1. Specific activities and keratin/casein ratios of the purified wild-type and mutant SAPB enzymes using keratin and casein as substrates.

SAPB enzyme	Bacillus subtilis DB430	Specific activity with keratin (U.mg⁻¹)^a ^, ^b	Relative specific activity to wild-type with keratin^c	Specific activity with casein (U.mg⁻¹)^a ^, ^b	Relative specific activity to wild-type with casein^c	Keratin/casein ratio
WT	pNZ1	62375±820	1.00	24950±640	1.00	2.50
L31I	pNZ7	15469±357	0.25	28125±663	1.12	0.55
T33S	pNZ8	19420±415	0.28	31321±668	1.25	0.62
N99Y	pNZ9	139012±999	2.22	34753±656	1.39	4.00
L31I/T33S	pNZ10	26345±643	0.34	37634±670	1.50	0.70
L31I/N99Y	pNZ11	54689±781	0.87	38911±684	1.55	1.40
T33S/N99Y	pNZ12	52340±770	0.83	40261±707	1.61	1.30
L31I/T33S/N99Y	pNZ2	29052±665	0.46	45500±755	1.82	0.63

Specific 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).

The experiments were conducted three times and ± standard errors are reported.

The relative activity is calculated by taking the specific activity of the wild-type as 1.00.