Table 1.

Properties of selected Ca²⁺-binding proteins (adapted from Schwaller 2009).

	α PV	β PV (OM)	CB-D9k	CB-D28k	CR
Ca2+-binding sites (functional)	3 (2)	3 (2)	2 (2)	6 (4)	6 (5)
Ca2+-specific/ mixed Ca2+/Mg2+ sites	0/2	1/1	2/0	4/0a	5/0
KD,Ca (nM)	4–9b	Mixed: 42–45d	KD1 ≈ 200–500e KD2 ≈ 60–300	high aff. (h)f KD1 ≈ 180–240	KD(T) 28 µMg KD(R) 68 KD(app) 1.4 µM
		Ca2+-specific: 590–780d		medium aff. (m) KD2 ≈ 410–510	EF5: 36 µM
KD,Mg	≈ 30 µMb	160–250 µMd		714 µMa	4.5 mMh
KD,Ca(app) (nM) at [Mg2+] of 0.5–1 mM	150–250c	230–310c
kon,Ca (µM−1s−1)	6b		up to 1000i	h sites ≈ 12f	T sites: 1.8g
				m sites ≈ 82	R sites: 310
kon,Mg (µM−1s−1)	0.1–1c				site EF5: 7.3
cooperativity	nok	? yesl	yesm	yes	yes
				nH ≈ 1.1–1.2a	nH ≈ 1.3–1.9g
DCabuffer (µm2s−1)	37–43n			>100o	≈ 25p
	∼12			≈ 25

^aAlthough considered as Ca²⁺-specific, at physiological [Mg²⁺]_i, the apparent Ca²⁺ affinity is approximately two-fold lower (Berggard et al. 2002a).

^b(Eberhard and Erne 1994).

^cK_D,Ca and k_on for PV are [Mg²⁺] dependent; calculated values are estimates at [Mg²⁺]_i 0.6–0.9 mM.

^d(Cox et al. 1990).

^e(Linse et al. 1991).

^fCB-D28k has high-affinity (h) and medium-affinity (m) sites, the stochiometry h/m is either 2/2 or 3/1 (Nagerl et al. 2000).

^gFor details, see text and Faas et al. (2007).

^h(Stevens and Rogers 1997).

ⁱThe value represents the diffusion limit, assuming a maximal Ca²⁺ diffusion rate of ≈ 200 µm²s⁻¹ (Martin et al. 1990).

^kPV has 2 essentially identical Ca²⁺-binding sites with n_H close to 1.

^l(Yin et al. 2006).

^m(Akke et al. 1991).

ⁿThe diffusion coefficients D_Cabuffer for PV in muscle myoplasm (37 µm²s⁻¹) (Maughan and Godt 1999) and Purkinje cell dendrites of 43 µm²s⁻¹; (Schmidt et al. 2003a); smaller values are measured in PC soma and axons (≈12 µm²s⁻¹); (Schmidt et al. 2007a).

^oCB-D28k’s mobility in PC dendrites is 26 µm²s⁻¹ (Schmidt et al. 2005), clearly slower than in water (Gabso et al. 1997), and also slower than PV in PC dendrites.

^pEstimation based on the similar size of CB-D28k and CR.