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. Author manuscript; available in PMC: 2013 Feb 1.
Published in final edited form as: J Inorg Biochem. 2011 Nov 19;107(1):111–118. doi: 10.1016/j.jinorgbio.2011.11.004

Table 1.

Properties of Gd-DTPA, ProCA1 and its PEGylated variants.

Sample Gd-DTPA ProCA1 ProCA1
PEG0.6k		 ProCA1
PEG2.4k		 ProCA1
PEG12k
D - 13.9 12.9 12.1 6.5
Radius (Å) - 16.9 18.2 19.4 40.2
Log Ka 18.4[11] 11.46 11.26 11.70 11.08
q 1.1[30] 2.4 3.2 3.0 2.6
r1 (mM−1 s−1) 4.5 23.8 39.5 47.6 83.8
r2 (mM−1 s−1) 5.2 43.7 92.5 98.7 100.8

D is the diffusion constant (×107 cm2 s−1) calculated from the Debye-Stokes-Einstein equation. The radius values were obtained by fitted data from the pulse-field-gradient NMR experiment. q is the water coordination number determined by measuring Tb3+ luminescence decay in H2O or D2O. Ka is the conditional association constant of contrast agents with Gd3+ and is the reciprocal of dissociation constant Kd (Kd = 1/Ka). Relaxation times were measured on the 0.47 T Mini Spec Relaxometer (Bruker).