ASTM E1759-95(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.

1.1 This test method covers the determination of isoaspartic acid residues in a protein or peptide sample. This test method is applicable for the determination of isoaspartic acid residues in a sample in the range of 2.5-50 μmol/L. Higher concentrations can be determined following dilution. The reported lower range is based on single-operator precision.

1.2 The values stated in SI units are to be regarded as the standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.