Continuous Electrospray Ionization Mass Spectrometry Assay for Measuring Phospholipase Activity against Liposomes

Area of Science:

• Biochemistry
• Enzymology
• Analytical Chemistry

Background:

• Phospholipases play crucial roles in lipid metabolism and cell membrane integrity.
• Animal venoms often contain phospholipases with potent neurotoxic or myotoxic effects.
• Existing assays for phospholipase activity are often discontinuous and analyze simple lipid substrates.

Purpose of the Study:

• To develop a temperature-controlled, continuous electrospray ionization mass spectrometry (ESI-MS) assay for measuring phospholipase A2 activity.
• To characterize the activity of paradoxin, a neurotoxic phospholipase A2 from inland taipan snake venom, against liposomes.
• To provide a more physiologically relevant method for studying enzyme kinetics with complex lipid substrates.

Main Methods:

• Development of a continuous ESI-MS assay for real-time measurement of phospholipase A2 activity.
• Utilized liposomes as a complex lipid substrate, mimicking natural conditions.
• Employed paradoxin from inland taipan snake venom as the model enzyme.

Main Results:

• The continuous ESI-MS assay successfully measured Michaelis-Menten parameters and confirmed the requirement for Ca2+.
• Assay conditions, such as metal ion concentration and temperature, influenced both enzyme activity and liposome substrate properties.
• Increased temperature affected liposome size, enhancing enzyme activity by increasing substrate accessibility.

Conclusions:

• A novel continuous ESI-MS assay provides a robust method for studying phospholipase A2 activity against complex liposomal substrates.
• The assay offers nuanced insights into enzyme-substrate interactions and the impact of environmental factors.
• This methodology is adaptable for analyzing other enzyme reactions involving complex lipid substrates.