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Protein Protocols Protein Protocols

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628 Weber and McFadden<br />

Fig. 2. Comparison of discontinuous acid gel with continuous acid gel. The following<br />

experiment tested for the presence of age-altered proteins in a commercial preparation of collagenase.<br />

The collagenase preparation (Sigma, type IV) was methylated with purified rabbit erythrocyte<br />

PCM and 3 H-AdoMet. Aliquots from the same methylation reaction were then resolved<br />

on (top) 12% discontinuous acid gel, described in text, or (bottom) 12% continuous acid gel<br />

system prepared according to the method of Fairbanks and Auruch (3). Lane 1: Rainbow molwt<br />

markers (Amersham); Lane 2: 18 µg of methylated collagenase were loaded on each gel.<br />

Following electrophoresis and staining, 0.5-cm gel slices were treated with base to detect<br />

radioactivity as described under Subheading 3. Both gel systems are capable of preventing the<br />

loss of methyl esters from protein samples, but the discontinuous system provides much higher<br />

resolution of individual polypeptide bands.<br />

4. Notes<br />

1. The buffering system employed in the stacking gel and sample solubilization buffer is<br />

based on a modification of the C & L buffering system. NaCl is employed rather than KCl<br />

of the original system, because K + ions cause SDS to precipitate out of solution.

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