Studies on the mechanism of insulin action. IV. The isolation and determination of a low insulin receptor activity.

After passing the membrane protein dissolved in 1% DOC over a Sepharose 4B column, a peak with insulin receptor binding activity has been shown in the void volumn. After treating this single peak fraction with 6M guanidine HCl and again passing over a Sepharose 4B column preequilibrated with guanidine HCl, four absorbing peaks at 280 nM have been observed. In addition to the first peak representing the void volume, the 4th absorbing peak has been found to display an obvious binding activity as well. This low molecular biologically active unit has also been demonstrated by means of gel electrophoresis. Its molecular weight has been determined with Sepharose 6B to be about 50,000 daltons.