Affinity labels for the anion-binding site in ovotransferrin.

Area of Science:

• Biochemistry
• Protein Chemistry
• Biophysical Chemistry

Background:

• Bromopyruvate was previously identified as an affinity label for ovotransferrin's anion-binding site.
• The mechanism of covalent attachment was presumed to be alkylation.

Purpose of the Study:

• To investigate the mechanism of anion binding to ovotransferrin.
• To explore the role of hydroxypyruvate in labeling ovotransferrin.
• To understand iron binding and release in ovotransferrin.

Main Methods:

• Chemical modification of ovotransferrin with hydroxypyruvate.
• Analysis of labeled ovotransferrin using model complexes and amino acid analysis.
• Investigation of iron release from ternary complexes at low pH.

Main Results:

• Hydroxypyruvate functions as an affinity label for ovotransferrin, similar to bromopyruvate.
• The labeling mechanism involves Schiff base formation and imine bond reduction with a lysine residue.
• Covalent attachment of anions increases iron retention in the ovotransferrin-iron-anion complex at low pH.

Conclusions:

• The irreversible labeling of ovotransferrin by anions is not solely due to alkylation.
• A Schiff base mechanism followed by reduction explains the covalent attachment.
• Labeled ovotransferrin can be used to study iron release mechanisms in lysosomal vesicles.