Solubilization of insulin binding and degrading activity from guinea pig kidneys

Insulin binding and degrading activities were solubilized by a nonionic detergent. Triton X-100, from guinea pig kidney particulate fractions (100,000 x g pellet). The solubilized insulin binding activity appeared as a single peak on Sepharose 6B gel filtration with a Stokes radius of 73 A. The pI of the solubilized insulin binding activity determined by flat-bed isoelectric focusing was 5.6. On the other hand, the Stokes radius of the solubilized moelcule with insulin degrading activity was 54 A by the same column with a pI of 5.2. More than 98% of the insulin binding activity could be adsorbed to a column of concanavalin A-agarose, while about 94% of the insulin degrading activity could not be adsorbed to this column. These results strongly suggest that the macromolecule for the insulin binding activity is not identical to that for the insulin degrading activity.