Immunological evidence that inactive renin is prorenin

Area of Science:

• Biochemistry
• Immunology
• Renal Physiology

Background:

• Human renin is a key enzyme in the renin-angiotensin-aldosterone system.
• Inactive renin, also known as prorenin, circulates in plasma and is found in tissues.
• Understanding the structural and immunochemical differences between active and inactive renin is crucial for studying its regulation.

Purpose of the Study:

• To characterize the immunochemical properties of an antibody raised against the human renin pro-segment.
• To investigate the recognition of active and inactive human renins by this antibody.
• To explore the conformational changes of inactive renin upon activation.

Main Methods:

• Generation of a synthetic dodecapeptide corresponding to the C-terminal portion of the human renin pro-segment.
• Production and use of an antibody against this pro-segment peptide.
• Detection of immune complexes using protein A-Sepharose precipitation.
• Testing antibody binding to purified active and inactive human renins.
• Assessing the effect of acid and trypsin activation on antibody binding.

Main Results:

• The anti-prorenin antibody specifically bound to inactive renin (both renal and plasma forms) but not to active renin.
• Antibody to active renin recognized both active and inactive forms.
• Acid activation reversibly enhanced the binding of inactive renin to the anti-prorenin antibody.
• Trypsin activation irreversibly reduced or abolished binding, suggesting conformational changes.

Conclusions:

• Inactive renin shares immunochemical determinants with prorenin.
• Acidification induces conformational changes in the pro-segment of inactive renin.
• Trypsin can convert inactive renin to active renin and intermediate forms with altered immunochemical properties.