. Author manuscript; available in PMC: 2012 Mar 1.

Published in final edited form as: Biochemistry. 2011 Feb 3;50(8):1336–1346. doi: 10.1021/bi101734q

Table 4.

Inactivation rate constants of pure human ASL enzymes and Pool 2 of the hybrid pairs at 60°C^a

Enzyme	k_i ± S.E (hr⁻¹)^b
His-tag WT	0.086 ± 0.004
His-tag L311V	0.059 ± 0.005
His-tag R396H	0.096 ± 0.007
His-tag R396C	0.103 ± 0.01
His-tag R194C	2.76 ± 0.1
Pool 2 of non-His-tag R396C/His-tag R194C	0.255 ± 0.02
Pool 2 of non-His-tag WT/His-tag WT	0.099 ± 0.003
Pool 2 of non-His-tag R396H/His-tag WT	0.101 ± 0.007
Pool 2 of non-His-tag R396H/His-tagL311V	0.122 ± 0.003

The enzyme samples (0.2 mg/ml) in fresh Enzyme Storage Buffer, pH 7.0, were incubated at 60 °C. Aliquots were removed periodically and the activity of was measured at 25 °C by addition of a 10 μl aliquot of enzyme to 1.0 ml solution containing 50 mM HEPES buffer, pH 7.4 and 60 μM of each substrate (SAMP).

The k_i value for each reaction was determined from the slope of ln (E_t/E₀) versus time. The E_t and E₀ are the specific activity at time t and zero, respectively. The values are shown along with their standard errors.