The submolar quantities of N-terminals in proteins. Effect of sodium dodecyl sulfate on the N-terminals of egg albumin and bovine, equine, and procine γ-globulins

Abstract

The quantities of the N -terminal amino acids of the proteins investigated were increased twofold to tenfold and more by action of sodium dodecyl sulfate in acid; serine and threonine were affected most. The limited action of trypsin caused an increase of the quantities of all the N -terminals of porcine γ-globulin. In all the cases investigated, although the quantities changed, no new N -terminal appeared beside the ones present in the untreated protein. The submolar quantities of the N -terminals of the proteins under study were not impurities; the increased quantities of N -terminals derived not from the uncovering of masked N -terminals because of denaturation, but more likely from a specific hydrolysis, which was catalyzed by trypsin and by the acidic alkyl sulfate. It is suggested that the N -terminals of a number of proteins may be the products of autolysis or hydrolysis (of particularly labile peptide bonds) which took place at various times during the physiological and laboratory history of the protein molecule.