Table 1.

Immobilization methods of MagMASS for all proteins investigated have an extremely high binding efficiency. Almost all of the protein for immobilization is available in the well for ligand binding.

RXRα Constructa	Matrixb	LG100268c	9-cis-Retinoic acidd	13-cis-Retinoic acid
		Enrichment ± Standard errore
MBP-RXRα NHS	Buffer only	17.2 ± 13.9 (N=9) p<0.01f	6.7 ± 1.7 (N=8) p<0.01	1.1 ± 0.1 (N=4) p>0.2
“	Compound library	42.4 ± 90.1 (N=8) p<0.01	5.6 ± 1.9 (N=8) p<0.01	0.9 ± 0.1 (N=5) p>0.2
“	P. palustris extract	298.6 ± 459.7 (N=7) p<0.01	24.3 ± 7.2 (N=6) p<0.01	N/A (N=4) p>0.2
“	S. nigricans extract	72.5 ± 49.8 (N=4) p<0.01	12.0 ± 4.6 (N=3) p<0.05	N/A (N=4) p>0.2
MBP-RXRα amylose	Buffer only	8.6 ± 2.0 (N=4) p<0.01	2.8 ± 0.9 (N=8) p=0.22	0.9 ± 0.1 (N=5) p>0.2
“	Compound library	10.5 ± 4.2 (N=7) p<0.01	1.9 ± 0.4 (N=8) p=0.06	1.6 ± 0.3 (N=4) p>0.2
“	P. palustris extract	56.8 ± 34.3 (N=9) p<0.01	9.5 ± 2.2 (N=9) p<0.01	N/A (N=5) p>0.2
“	S. nigricans extract	59.0 ± 47.0 (N=4) p<0.01	6.1 ± 2.2 (N=4) p<0.05	N/A (N=5) p>0.2

^aMBP-RXRα was immobilized using either covalent attachment of amino groups via NHS on the magnetic beads or through non-covalent interaction between MPB and amylose beads.

^bPossible interference of ligand binding to MBP-RXRα was investigated using different matrices ranging from simple buffer to complex botanical extracts.

^cA positive control, LG100268 was used as a high affinity synthetic ligand of RXRα (Kd 3 nM [26])

^d9-cis-Retinoic was tested as an endogenous ligand for RXRα (Kd 15.7 nM [25]), while isomeric 13-cis retinoic was used as a non-binding negative control [25].

^eThe enrichment factor (peak area compound bound to RXRα/ peak area compound bound to denatured protein) was averaged over all replicates.

^fOne-way paired t-test was used to evaluate the difference between results obtained using active RXRα and denatured protein.