Regulation of the post-translational conjugation of amino acids to rat brain proteins

Abstract

Post-translational conjugation of arginine (but not other amino acids) to proteins has been reported to occur in a high speed supernatant fraction of rat brain homogenates from which molecules of less than 5000 mol. wt have been removed. In the present study we report that removal of molecules of less than 1000 mol. wt by dialysis, does not result in incorporation of arginine into protein in amounts significantly different than in the undialysed supernatant. The addition of molecules with molecular weights greater than 1000 and less than 5000 to the active fraction, inhibits the incorporation of arginine into proteins in a concentration dependent manner suggesting that the post-translational incorporation of arginine into brain is regulated by a molecule(s) of greater than 1000 and less than 5000 mol. wt. Incorporation of lysine into proteins did not occur following removal of molecules of less than 5000 mol. wt, but did occur in the void volume fraction of a Sephacryl S-200 column (molecular weight cut-off 125,000), suggesting that the incorporation of lysine into proteins is regulated by molecules retained by the S-200 column but greater than 5000 mol. wt. When experiments were repeated using the void volume of a Sephacryl S-300 column (molecular weight exclusion, ~ 200 k), leucine and proline were incorporated in amounts similar to arginine and lysine, and serine, alanine, valine, phenylalanine and histidine were incorporated at lower but measurable levels. The data are interpreted as indicating the presence of regulatory molecules in vivo and in the high speed supernatant of rat brain, which can be removed by molecular weight exclusion chromatography and control the post-translational incorporation of individual amino acids into proteins. Comparison of the proteins modified by arginine and lysine using two-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis indicates that there exists a group of proteins modified by arginine, another group modified by lysine, and a third group which is modified by both arginine and lysine.