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. Author manuscript; available in PMC: 2007 Sep 25.
Published in final edited form as: J Mol Biol. 2007 Feb 9;368(2):434–449. doi: 10.1016/j.jmb.2007.02.005

Table 4.

Rate constants for the binding of hRI to RNase 1 and its variants

RNase 1 kd (s-1) ka (M-1 s-1)
wild-type (9.9 ± 0.7) ×10-8 a 3.4×108 b
R39D/N67D/N88A/G89D/R91D 0.22 ± 0.03 c (2.2×106) 1.2 × 105 d (2.8×103)
R39L/N67L/N88A/G89L/R91L 0.092 ± 0.003 c (9.3×105) 3.1 × 106 d (1.1×102)
a

The value of kd (±SE) was determined by following the release of diethylfluorescein- labeled RNase 1 from hRI over time and fitting the curve to equation (3).

b

The value of ka is from ref 35. Both angiogenin and RNase A have association rates within twofold of each other,35 and so the association rate of RNase A was chosen for comparison due to the greater similarity of its sequence and structure with those of RNase 1.

c

Values of kd (±SE) were determined by following the release of a fluorescein-labeled RNase 1 variant from hRI over time and fitting the curves to equation (3). Values in parentheses represent the fold increase from wild-type RNase 1.

d

Values of ka were calculated with the equation: Kd = kd/ka. Numbers in parentheses represent the fold decrease from wild-type RNase 1.