Effect of concanavalin A on membrane-bound enzymes from mouse lymphocytes

Area of Science:

• Biochemistry
• Cell Biology
• Immunology

Background:

• Lymphocytes play a crucial role in the immune system.
• Enzymes like Mg2+-ATPase and (Na+ +K+)-ATPase are vital for cellular functions.
• Understanding their activity in lymphocytes can shed light on immune responses.

Purpose of the Study:

• To investigate the ionic influence and ouabain sensitivity of lymphocyte Mg2+-ATPase and (Na+ +K+)-ATPase.
• To determine the localization of active sites for these enzymes.
• To explore the effect of concanavalin A on enzyme activity and its relation to lymphocyte stimulation.

Main Methods:

• Studied enzyme activity in intact cells, microsomal fractions, and isolated plasma membranes.
• Utilized ouabain sensitivity as an indicator for (Na+ +K+)-ATPase.
• Assessed the impact of concanavalin A (a mitogen) on enzyme kinetics.

Main Results:

• The active site of Mg2+-ATPase and 5'-nucleotidase is on the external plasma membrane side; the ATP binding site of (Na+ +K+)-ATPase is internal.
• Concanavalin A stimulated both Mg2+-APTase and (Na+ +K+)-ATPase in intact cells and plasma membranes.
• Thymocyte Mg2+-ATPase showed higher stimulation by concanavalin A compared to spleen lymphocytes, while (Na+ +K+)-ATPase was undetectable in thymocytes.

Conclusions:

• Mg2+-ATPase and (Na+ +K+)-ATPase are present in lymphocyte plasma membranes with distinct site localizations.
• Concanavalin A significantly stimulates lymphocyte Mg2+-ATPase and (Na+ +K+)-ATPase activities.
• The observed enzyme stimulation by concanavalin A suggests a potential role in lymphocyte blast transformation and activation.