Low pH stability of alpha-1-antititrypsin.

Area of Science:

• Biochemistry
• Protein Chemistry

Background:

• Alpha-1-antitrypsin (AAT) is a key protease inhibitor.
• AAT loses trypsin inhibitory capacity irreversibly below pH 5.0.

Purpose of the Study:

• To investigate the regeneration of alpha-1-antitrypsin's inhibitory activity.
• To characterize the structural changes affecting AAT activity in different pH conditions.

Main Methods:

• Titration of acidified AAT to basic media (pH 8.0).
• Fluorescence spectroscopy to monitor spectral changes.
• Sephadex gel filtration to assess protein aggregation.
• Isolation of monomeric and polymeric AAT forms.

Main Results:

• Significant regeneration of AAT inhibitory activity observed upon titration to basic pH.
• Activity recovery correlated with decreased fluorescence at 335 nm.
• Acidic conditions (especially near pH 4.0) induced time-dependent protein aggregation.
• Isolated monomeric AAT showed high activity recovery, while aggregates retained immunological reactivity but lost inhibitory function.

Conclusions:

• Alpha-1-antitrypsin's inhibitory activity can be regenerated after acid-induced denaturation.
• Protein aggregation in acidic media is linked to loss of enzyme inhibitory function.
• Monomeric AAT is crucial for maintaining biological activity, whereas aggregated forms are less functional.