Bovine myeloperoxidase and lactoperoxidase each contain a high affinity site for calcium

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Bovine myeloperoxidase and lactoperoxidase are heme-containing enzymes.
• The role of metal ions, particularly calcium, in peroxidase structure and function is not fully understood.
• Previous studies have not identified calcium as a significant component of these enzymes.

Purpose of the Study:

• To investigate the presence and role of calcium in bovine myeloperoxidase and lactoperoxidase.
• To identify potential calcium-binding sites in human myeloperoxidase.

Main Methods:

• Elemental analysis to determine metal content.
• Protein denaturation using guanidine hydrochloride and EGTA to assess calcium binding affinity.
• Bioinformatic analysis of human myeloperoxidase amino acid sequences to predict calcium-binding sites.

Main Results:

• Bovine myeloperoxidase and lactoperoxidase contain one calcium ion per iron atom.
• Calcium is tightly bound and its removal by guanidine hydrochloride/EGTA causes protein precipitation.
• Computer analysis identified two potential calcium-binding sites in human myeloperoxidase.

Conclusions:

• Calcium is an integral component of bovine and lactoperoxidase, binding with high affinity.
• The findings suggest a structural or functional role for calcium in these enzymes.
• This study presents the first evidence for calcium in these peroxidases and offers insights into potential calcium-binding mechanisms in human myeloperoxidase.