The separation of alpha-2 macroglobulin into five components with differing electrophoretic and enzyme-binding...

Area of Science:

• Biochemistry
• Proteomics
• Enzymology

Background:

• Alpha-2 macroglobulin (A2M) is a large plasma proteinase inhibitor.
• Its interaction with proteases is crucial for regulating biological processes.
• Understanding A2M heterogeneity and protease binding is key to its function.

Purpose of the Study:

• To isolate and characterize human alpha-2 macroglobulin.
• To investigate the electrophoretic heterogeneity of A2M.
• To elucidate the binding characteristics of A2M with trypsin and chymotrypsin.

Main Methods:

• Gel filtration (Bio-Gel P-300, A5m) for A2M isolation.
• Ultracentrifugation (sedimentation velocity and equilibrium) for molecular weight determination.
• Immunoelectrophoresis and acrylamide gel electrophoresis for purity and heterogeneity analysis.
• Enzyme binding assays with trypsin and chymotrypsin.

Main Results:

• A2M was isolated as a homogeneous protein (mol wt 650,000).
• Electrophoresis revealed multiple A2M species, with enzyme binding altering mobility.
• Slower species bound enzymes, while faster species were enzyme-bound or inactive.
• A2M bound maximally 2 moles of trypsin or 1 mole of chymotrypsin.
• Chymotrypsin binding inhibited subsequent trypsin binding.

Conclusions:

• Human alpha-2 macroglobulin exists in multiple electrophoretic forms.
• Enzyme binding induces conformational changes affecting A2M mobility.
• Chymotrypsin binding to A2M results in a stable, fast-moving complex that prevents further protease interaction.