Evaluation of the Free Electrophoretic Mobility at an Ionic Strength of 01 mol L

For reasons of comparability, the free electrophoretic mobility obtained for a given set of experimental conditions may be corrected to an effective mobility at an ionic strength of 0.1 mol L"1. This can be achieved by substituting the relevant values into Abramson's equation:

Uo.i = (U>o.I(k>O.I xRs + 2.4)) x (kO.I XRs + 2.4)-1

where U0.1 and U>0.1 (m2 V-1 s_1) represent the free electrophoretic mobilities at an ionic strength of 0.1 (mol m~3) and > 0.1 (mol m~3) respectively; k>0.1 and k0.1 represent the reciprocal of the effective thickness of the ionic cloud at ionic strength of 0.1 (mol m~3) and > 0.1 (mol m~3) respectively and RS (m) is the Stokes radius of the protein. For the experimental conditions given earlier:

thus:

Taking ferritin as an example, for which U (m2 V-1 s_1) = 3.28 x 10~9 (at I = 0.529 x 103 (mol m-3), if k>0.1 = 2.3 6684 2 604 x 109 and Rs = 6.20 x 10-9 (m) are determined and substituted into eqn [48], it follows that:

U0.1 = ((3.28 x 10-9) x (2.366842604 x 109 x 6.20 x 10-9 # 2.4)) x (1.02930525 x 109 x 6.20 x 10-9 + 2.4)-1 [51]

thus:

The free electrophoretic mobilities at I = 0.52875 x 103 (mol m-3) and at I = 0.1 x 103 (mol m© of several marker proteins and some carbonic anhydrase isozymes are listed in Table 10.

Table 10 Free electrophoretic mobility of ferritin in buffered solution

Experimental conditions Free mobility Reference

Table 10 Free electrophoretic mobility of ferritin in buffered solution

Experimental conditions Free mobility Reference

Moving boundary method = 0.1 (mol L-1), 0 (0C), pH 8.6

-6.1

Mazur etal. (1950)

Agarose gel electrophoresis I = 0.05 (mol L-1), # 20 fC), pH 6.8

- 10.5

Gosh et al. (1974)

Disc electrophoresis C = 2%; 0 (0C), pH 8.88 I = 0.0034 (mol L-1) I = 0.10 (mol L-1)

- 10.97 -5.67

Rodbard etal. (1971)

PA gradient gel electrophoresis

5-30 T(%), acrylamide-Bis = 24 :1; #4 (0C), pH 8.4a

I = 0.10 (mol L-1)

-3.28 -6.38

Rothe (1991)

a Electrophoretic conditions; 90 mmol L~1 Tris, 80 mmol L~1 boric acid, 1.25 mmol L~1 EDTA-Na2, pH 8.4; separation distance 73 mm, voltage gradient 41.1 (VcmT1) References are given in Rothe (1991).

a Electrophoretic conditions; 90 mmol L~1 Tris, 80 mmol L~1 boric acid, 1.25 mmol L~1 EDTA-Na2, pH 8.4; separation distance 73 mm, voltage gradient 41.1 (VcmT1) References are given in Rothe (1991).

The result of calculating the net protonic charge of a protein of course remains unaffected whether the ionic strength of the experiment or that of a buffer strength of 0.1 mol L"1 is used.

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