Table 1.

Heparin-binding affinity estimates of TGF-β superfamily cytokines.

Protein	Heparin Affinity		Reference
TGF-β1	HAC	≥0.5 M	[13]
TGF-β2	HAC	≥0.5 M	[13]
BMPs/GDFs
BMP-2	SPR	Kd 20 nM	[14]
BMP-4	n.d.		-
BMP-6	n.d.		-
BMP-7	HAC	0.5 M	[15]
BMP-14/GDF-5	SPR	Kd 50 nM	[16]
BMP-15/GDF-9	HAC	≈1.0 M	[17]
Neurotrophins
GDNF	HAC	0.8 M	[18]
	SPR	Kd 23 nM	[19]
Artemin	HAC	23 nM	[18]
	SPR	Kd 45 nM	[19]
Neurturin	HAC	1.2 M	[18]
	SPR	Kd 115 nM	[19]
Can family antagonists
Gremlin-1	HAC	0.8 M	[20]
	SPR	Kd 20 nM	[21]
Gremlin-2/PRDC	HAC	0.67 M	[22]
Sclerostin	n.d		-
Other antagonists
Noggin	HAC	0.8 M	[23]
Chordin	HAC	1.0 M	[24]
Follistatin (288 isoform)	SPR	Kd 1.0 M	[25]

The techniques have been employed: heparin affinity chromatography, HAC, and surface plasmon resonance (SPR). HAC employs a NaCl gradient to elute the bound cytokine, and the concentration of salt required is given. This approach therefore investigates the ionic component of the binding interaction. For SPR, the estimated dissociation constant is presented. In comparing estimates from the different studies, it must be borne in mind that different laboratories will have used a variety of heparin immobilisation procedures and different batches of heparin.