Table 3. Overview of Experimentally Determined Thermodynamic Constants Describing the Affinity of Metalloproteins for Select Trivalent Actinides (Ac³⁺, Am³⁺, Cm³⁺, and Cf³⁺), as well as for Tetravalent Actinides (Th⁴⁺ and Pu⁴⁺) and Uranyl (UO₂²⁺)^a.

protein	reaction	thermodynamic constant	conditions	ref
transferrin (Tf)	Pu4+ + Tf = PuCTf	log K11 = 24.8	pH 6.0, synergistic ion = NTA. I = 0.1 M NaCl, MES buffer	(96)
	Pu4+ + Tf = PuCTf	log K11 = 26.44	pH 7.0, synergistic ion = NTA. I = 0.1 M	(99)
	Fe3+ + Tf = Fe2Tf	log K11 = 21.4	pH 7.4, Ambient pCO2.	(37)
	Fe3+ + FeTf = Fe2Tf	log K21 = 20.3
	2 Fe3+ + Tf = Fe2Tf	log β21 = 41.7
	Cm3+ + Tf = CmCTf	log K11 = 8.8 (C-lobe)	pH 8.6, 50 mM Tris, 150 mM NaCl, 5 mM NaHCO3	(38)
	Cm3+ + CmCTf = Cm2Tf	log K21 = 7.0 (N-lobe)
	2 Cm3+ + Tf = Cm2Tf	log β21 = 15.8
	2 Ac3+ + Tf = Ac2Tf	log β21 = 10.9	Estimate based on literature data and a linear free-energy relationship.	(119)
fetuin (Fet)	Pu4+ + Fet = PuFet	log K11 = 26.2	pH 7.0. I = 0.1 M	(99)
	UO22+ + Fet = UO2Fet	log K11 = 7.5 (Kd = 30 nM)	pH 7.4, 140 mM NaCl, pCO2	(97)
human serum albumin (HSA)	Th4+ + HSA = ThHSA	log K11 = 4.12	pH ∼7.4, 5 mM HEPES, 150 mM NaCl	(100)
	UO22+ + HSA = UO2HSA	log K11 = 4.27	pH ∼7.4, 5 mM HEPES, 150 mM NaCl	(100)
lanmodulin (LanM)	wild-type lanmodulin: 3 Ac3+ + LanM = Ac3LanM	log β31 = 36.2	pH 7.0, 90 mM NaCl, 10 mM HEPES	(119)
	wild-type lanmodulin: 3 Am3+ + LanM = Am3LanM	log β31 = 35.6	pH 5.0, 75 mM NaCl, 25 mM acetate	(50)
	3 Cm3+ + LanM = Cm3LanM	log β31 = 35.8	pH 5.0, 75 mM NaCl, 25 mM acetate	(50)
	lanmodulin variants:	log β31 = 34.4	pH 5.0, 75 mM NaCl, 25 mM acetate	(120)
	3 Am3+ + 3D9N = Am33D9N
	3 Am3+ + 3D9A = Am33D9A	log β31 = 33.1
	3 Am3+ + 3D9M = Am33D9M	log β31 = 32.3
	3 Am3+ + 3D9SeMet = Am33D9SeMet	log β31 = 32.4
	3 Am3+ + 3D9H = Am33D9H	log β31 = 32.6
alpha amylase (Amy)	Cm3+ + Amy = CmAmy	log K11 = 4.76	pH 5.5, I = 0.1 M	(105)
	Cm3+ + 3 Amy = Cm(Amy)3	log β13 = 12.14
	UO22+ + Amy = UO2Amy	log K11 = 5.67	I = 0.1 M (NaCl)	(107)
	UO22+ + 2 Amy = UO2(Amy)2	log β12 = 10.39
	UO22+ + Amy + HO– = UO2(HO)Amy	log K11–1 = 0.64
	UO22+ + Amy +2 HO– = UO2(HO)2Amy	log β11–2 = −6.28
osteopontin (OPN)	x UO22+ + OPN = (UO2)xOPN	(Kd = 26 nM)*	*Number of binding sites undetermined.	(103)
siderocalin (Scn)	[PuIVEnterobactin]2– + Scn = [PuIVEnterobactin]/Scn	log K11 = 10.0 (Kd = 0.09 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to enterobactin.	(102)
	[FeIIIEnterobactin]2– + Scn = [FeIiiEnterobactin]/Scn	log K11 = 9.4 (Kd = 0.41 nM)	pH 7.4, TRIS buffer, 32 μg/mL ubiquitin.	(121)
	[AmEnterobactin]3– + Scn = [AmEnterobactin]/Scn	log K11 = 9.6 (Kd = 0.24 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to enterobactin.	(102)
	[CmEnterobactin]3– + Scn = [CmEnterobactin]/Scn	log K11 = 9.7 (Kd = 0.20 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to enterobactin.	(102)
	[Am343-LI(1,2-HOPO)]− + Scn = [Am343-LI(1,2-HOPO)]/Scn	log K11 = 7.5 (Kd = 29 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to ligand.	(102)
	[Cm343-LI(1,2-HOPO)]− + Scn = [Cm343-LI(1,2-HOPO)]/Scn	log K11 = 7.5 (Kd = 32 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to ligand.	(102)
	[Cf343-LI(1,2-HOPO)]− + Scn = [Cf343-LI(1,2-HOPO)]/Scn	log K11 = 7.3 (Kd = 50 nM)	pH 7.4, TBS buffer, 10 μg/mL ubiquitin, 5% DMSO. Actinide precomplexed to ligand.	(23)
synthetic peptides (LBT)	Am3+ + LBT = AmLBT	log K11 = 7.35 (Kd = 45 nM)	pH 7, 10 mM HEPES/100 mM NaCl buffer,	(122)

^aCorresponding constants for ferric iron (Fe³⁺) are also given for comparison. Although not proteins, synthetic lanthanide peptides (LBTs) are also shown for the sake of comparison. The K_d values reported in this table correspond to protein binding constants, not solubility products (also abbreviated K_d in the literature).