Reactive thiol groups in calf-intestinal alkaline phosphatase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Calf intestinal alkaline phosphatase (CIAP) is a key enzyme in biological systems.
• Understanding enzyme kinetics and modification is crucial for biochemical research.

Purpose of the Study:

• To investigate the effects of iodoacetamide on calf intestinal alkaline phosphatase activity.
• To elucidate the mechanism of enzyme inactivation and activation by iodoacetamide.

Main Methods:

• Incubation of CIAP with varying concentrations of iodoacetamide.
• Measurement of enzyme catalytic activity over time.
• Analysis of kinetic parameters (Vmax) and iodoacetamide incorporation.

Main Results:

• Iodoacetamide induced time-dependent changes in CIAP activity, including both inactivation (above 2 mmol/l) and activation (lower concentrations).
• These alterations were irreversible, affected Vmax exclusively, and were independent of the presence of the substrate analogue Pi.
• Enzyme inactivation correlated with iodoacetamide incorporation, with significant activity loss occurring after modification of a single subunit, indicating a cooperative process.

Conclusions:

• Iodoacetamide is a potent modifier of calf intestinal alkaline phosphatase.
• Enzyme activity modulation by iodoacetamide involves irreversible changes affecting Vmax.
• Cooperative interactions between enzyme subunits likely mediate the observed activity loss, highlighting the importance of quaternary structure in enzyme function.