Beta-hydroxyaspartic acid in vitamin K-dependent proteins.

Area of Science:

• Biochemistry
• Analytical Chemistry
• Proteomics

Background:

• Beta-hydroxyaspartic acid is a non-standard amino acid found in certain proteins.
• Accurate quantitation of beta-hydroxyaspartic acid is crucial for understanding protein function, particularly in vitamin K-dependent proteins.

Purpose of the Study:

• To develop and validate a sensitive method for the accurate quantitation of beta-hydroxyaspartic acid in protein hydrolysates.
• To determine the presence and quantity of beta-hydroxyaspartic acid in various vitamin K-dependent proteins.

Main Methods:

• Protein hydrolysis using 6 M HCl to release beta-hydroxyaspartic acid.
• Quantitation using an automatic amino acid analyzer with a pH 2.0 eluting buffer.
• Detection via postcolumn reaction with o-phthalaldehyde, achieving a sensitivity of approximately 0.01 nmol.

Main Results:

• The method successfully quantifies beta-hydroxyaspartic acid with high sensitivity.
• Vitamin K-dependent proteins factor IX, factor X, protein C, and protein Z contain approximately one residue of beta-hydroxyaspartic acid.
• Protein S contains two to three residues, while prothrombin and non-vitamin K-dependent proteins lack this amino acid.

Conclusions:

• A reliable and sensitive method for beta-hydroxyaspartic acid quantitation has been established.
• The distribution of beta-hydroxyaspartic acid varies among vitamin K-dependent proteins, suggesting distinct roles.
• This analytical approach is valuable for characterizing post-translational modifications in proteins.