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Table 2 NaK alpha-subunit-binding affinity profiles for various cardenolides and bufadienolides (K D ± SEM)

From: Hellebrin and its aglycone form hellebrigenin display similar in vitro growth inhibitory effects in cancer cells and binding profiles to the alpha subunits of the Na+/K+-ATPase

Compounds Affinity (nM) Selectivity
α-1 α-2 α-3 α-1 / α-2 α-1 / α-3
Cardenolides
Ouabain 50 ± 10 70 ± 12 50 ± 7 0.7 1.0
Digoxin 104 ± 11 25 ± 4 27 ± 2 4.2 3.9
Uzarigenin-rhamnoside 90 ± 20 96 ± 7 122 ± 9 0.9 0.7
Uzarigenin 1,100 ± 120 883 ± 56 1,278 ± 142 1.3 0.9
Gitoxin 123 ± 8 85 ± 3 108 ± 17 1.5 1.1
Gitoxigenin 500 ± 90 1,180 ± 190 1,050 ± 100 0.4 0.5
Bufadienolides
Gamabufotalin-rhamnoside 30 ± 7 36 ± 10 17 ± 2 0.8 1.8
Gamabufotalin 243 ± 48 247 ± 30 236 ± 14 1.0 1.0
Hellebrin 86 ± 18 218 ± 52 175 ± 20 0.4 0.5
Hellebrigenin 103 ± 19 198 ± 51 191 ± 23 0.5 0.5
  1. *The data were obtained from three independent experiments.
  2. *The data for uzarigenin, uzarigenin-rhamnoside, gitoxigenin and gitoxin are from Katz et al. [5] and are included here.
  3. *Ouabain binding affinities for the three isoforms appear lower than analyzed previously [5]. The lower values in [5] are the result of full Scatchard analysis for ouabain which excludes all non-specific binding. The selectivity is the same even though the absolute values of KD are higher. All the experiments were done in the same way, e.g. we have left all the values obtained in the displacement experiments.