Basic amino acids preferring broad specificity aminopeptidase from human erythrocytes

Area of Science:

• Biochemistry
• Enzymology
• Human Physiology

Background:

• Cytosolic aminopeptidases play crucial roles in cellular protein turnover and peptide metabolism.
• Human erythrocytes contain various peptidases, but their specific functions and properties require detailed characterization.

Purpose of the Study:

• To purify and characterize a novel aminopeptidase from human erythrocyte cytosol.
• To determine the substrate specificity, kinetic properties, and molecular characteristics of the purified enzyme.

Main Methods:

• Purification of the aminopeptidase using chromatographic techniques.
• Enzyme activity assays with various aminoacyl naphthylamides and oligopeptides.
• Determination of molecular weight (M(r)) and isoelectric point (pI).
• Inhibition studies using specific enzyme inhibitors and metal chelators.

Main Results:

• A monomeric aminopeptidase (M(r) ~110,000, pI ~4.8) was purified.
• The enzyme exhibited a preference for N-terminal Lysine (Lys) and Arginine (Arg), with significant activity against di- to tridecapeptides.
• Substrates included Lys-bradykinin, angiotensin III, thymopentin, and enkephalins, indicating broad specificity.
• Enzyme activity was enhanced by Cobalt ions (Co2+) and inhibited by EDTA, pHMB, amastatin, bestatin, and puromycin.

Conclusions:

• The purified enzyme is a cytosolic, Lys(Arg)-preferring aminopeptidase with broad substrate specificity.
• Its ability to hydrolyze biologically relevant peptides suggests a role in erythrocyte peptide processing.
• The enzyme's characteristics provide insights into the enzymatic machinery within human red blood cells.