Table 1.

Mus81-Mms4 kinetic parameters on DNA joint molecules

Substrate	Vmax (nM/min)	KM (nM)	kcat (min−1)	Catalytic cycle (min)	kcat/KMa (nM−1 min−1)
3′-FL	4.9 ± 0.7	5.5 ± 2.6	0.97	1.03	0.19
RF-like	6.7 ± 0.6	7.3 ± 2.0	1.35	0.74	0.19
nXO12	6.0 ± 1.7	3.1 ± 2.0	1.20	0.83	0.39
pXO12-3′	1.6 ± 0.2	5.6 ± 1.8	0.32	3.13	0.06
DL	0.5 ± 0.2	1.2 ± 1.6	0.09	10.75	0.08
Y	1.3 ± 0.04	30.4 ± 11.3	0.26	3.85	0.009
XO12	−b
X12	−b

^ak_cat/K_M traditionally defines a ‘selectivity coefficient’ that can be used to rank substrates for their relative ‘selectability’ by an enzyme. In this case, nXO12 > 3′-FL′ ∼ RF-like > DL > pXO12-3′ > Y.

^bThe catalytic parameters could not be determined because of the negligible activity on these substrates.