TABLE 1.

Comparison between the propensity of various azurin species to binding ANS in ice at −13°C and the instability of the native fold to freeze-thawing

Azurin	Kd (mM)*	n†	(1 − fN)‡
WT	7.0	1.6	0.28
C3A/C26A	3.0	2.9	0.46
I7S	3.2	6.1	0.64
F110S	5.2	7.4	0.62

^*K_d, average apparent dissociation constant for ANS binding to azurin.

^†n, minimum number of bound, highly fluorescent ANS molecules.

^‡(1 − f_N), nonnative fraction of azurin after 15 freeze-thawing cycles.