Surface charge measurements on Micrococcus lysodeikticus and the catalytic implications for lysozyme

Area of Science:

• Microbiology
• Biochemistry
• Physical Chemistry

Background:

• Micrococcus lysodeikticus possesses a negatively charged cell wall.
• Lysozyme's lytic activity is crucial for bacterial cell wall degradation.
• Understanding electrostatic interactions is key to enzyme kinetics.

Purpose of the Study:

• To quantitatively analyze the influence of the cell wall's electrostatic field on lysozyme's lytic activity.
• To elucidate the role of ionic strength and pH on lysozyme-cell wall interactions.
• To investigate the charge properties of the lysozyme molecule at its active site.

Main Methods:

• Electrophoresis measurements of Micrococcus lysodeikticus.
• Quantitative analysis of electrostatic field effects.
• Assessment of lysozyme lytic activity under varying ionic strengths and pH.

Main Results:

• Micrococcus lysodeikticus cell wall exhibits a constant negative surface charge density (-1.5 microC/cm2) across pH 4-8.
• A local pH gradient is formed at the cell wall due to electrostatic interactions.
• At high ionic strengths, lysozyme activity is driven by electrostatic attraction; at low ionic strengths, repulsion dominates.

Conclusions:

• Electrostatic forces significantly modulate lysozyme's lytic activity.
• The negative charge on the lysozyme molecule, potentially at the Asp-52 residue, influences interactions at low ionic strengths.
• Counter-ion screening effects are critical in understanding charge distribution and enzyme activity at the cell surface.