Standard Test Method for Isoaspartic Acid in Proteins: Method for the Determination of Asparagine Deamidation Products (Withdrawn 2003)

Isoaspartic acid residues are generated during incubation of proteins under a wide variety of conditions in aqueous solution. Such residues are generated most commonly through the deamidation of aspargine residues although some reports of isoaspartic acid formation through the rearrangement of aspartic acid residues have been published.

The presence of such residues can indicate that the protein containing such residues has suffered damage that may affect the biological activity of the protein. The precise correlation between the level of isoaspartic acid content and the biological activity of the protein needs to be determined on a case by case basis.

The test measures the level of isoaspartic acid content in a protein sample. This level will often be correlated with the degree to which the protein has suffered deamidation at asparagine residues. In addition, isoaspartic acid residues can arise on occasion through the rearrangement of aspartic acid residues. For these reasons, the level of isoaspartic acid residues in proteins can be used as a general indication that the protein sample has suffered some level of damage and should not be interpreted to indicate the precise level of damage to any one region within a protein without further testing.