Determination of molecular weights and Stokes' radii of non‐denatured proteins by polyacrylamide gradient gel electrophoresis 3. Estimation of the upper and lower size limits of carbonic anhydrase as a model for complexing enzymes

Abstract

AbstractStudying the separation behavior of various native carbonic anhydrase isozymes from mammalian erythrocytes we found that the migration of these enzymes differs from that of the marker proteins commonly used in gradient gel electrophoresis. In alkaline buffer systems the enzymes from human, bovine, rabbit, and canine erythrocytes start to migrate with a size apparently 6 to 12 times larger than their monomeric size, then gradually lose in apparent size and finally end up in a size equivalent to their monomeric mol mass. We determined the monomeric mol mass of the various carbonic anhydrase forms to be 23 000 to 39 000 (g/mol). These values are in accordance with different data in the literature and the data which we obtained by sodium dodecyl sulfate‐gradient gel electrophoresis. The equations and the graphical solutions needed to calculate the apparent upper size as well as the monomeric size of mammalian carbonic anhydrases are presented. It is demonstrated by this example that only the time‐dependent version of non‐denaturing polyacrylamide gradient gel electrophoresis provides reliable mol mass estimations.