The mechanism of hydrolysis of beta-glycerophosphate by kidney alkaline phosphatase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Alkaline phosphatase (EC 3.1.3.1) is crucial for dephosphorylation reactions.
• Understanding its active site and regulatory mechanisms is vital for biochemical research.

Purpose of the Study:

• To elucidate the functional groups involved in pig kidney alkaline phosphatase activity.
• To investigate the kinetics and mechanisms of substrate binding, catalysis, and activation.

Main Methods:

• Enzyme kinetics studies across a pH range (6.6-10.3) and substrate concentrations (3 μM-30 mM).
• Investigation of inhibition by glutathione (GSH) and activation by magnesium ions (Mg2+).
• Analysis of functional group pKs and derivation of a reaction rate equation.

Main Results:

• Identified functional groups with pKs 7.0 and 9.1 involved in substrate binding.
• A group with pK 8.8 catalyzes conversion in its unprotonated form.
• Glutathione inhibits non-competitively by targeting Zn(II); Mg2+ binds to a group with pK 10.15.
• Mg2+ acts as an autosteric effector, with independent binding of substrate and Mg2+.

Conclusions:

• Detailed characterization of pig kidney alkaline phosphatase active site functional groups.
• Elucidation of the roles of pH, Mg2+, and GSH in enzyme activity and regulation.
• Proposed reaction mechanism and rate equation provide insights into enzyme function.