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Some catalytic and molecular properties of threonine deaminase from Bacillus stearothermophilus.

N Muramatsu, Y Nosoh

Journal of Biochemistry

|September 1, 1976

Summary

This summary is machine-generated.

Highly purified threonine deaminase from Bacillus stearothermophilus shows optimal activity at 65°C and pH 9.2-9.6. Its stability and regulatory properties, including allosteric inhibition by isoleucine, are detailed.

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Area of Science:

Biochemistry
Enzymology
Microbial Physiology

Background:

Threonine deaminase (EC 4.2.1.16) is a key enzyme in amino acid biosynthesis.
Understanding its properties in thermophilic bacteria provides insights into enzyme adaptation and regulation.

Purpose of the Study:

To highly purify threonine deaminase from Bacillus stearothermophilus.
To characterize its optimal activity, stability, and regulatory mechanisms, comparing them to related enzymes.

Main Methods:

Enzyme purification from Bacillus stearothermophilus.
Enzyme activity assays at varying temperatures and pH.
Stability studies under different conditions (dilution, storage, stabilizers).
Substrate saturation kinetics and allosteric regulation analysis (isoleucine, valine).
Determination of enzyme molecular weight and aggregation states.

Main Results:

Threonine deaminase exhibited maximum activity at 65°C and pH 9.2-9.6.
The enzyme was stabilized by egg albumin and isoleucine, particularly at pH 7.0.
Isoleucine induced sigmoidal substrate saturation kinetics (n=2), indicating allosteric regulation, with greater sensitivity at 40°C.
Valine showed slight inhibition, and its effect was antagonized by isoleucine.
The enzyme existed in two molecular forms (1.5-5 x 10^6 and 2 x 10^5 Da) that interconverted based on pH, temperature, and ligand presence.

Conclusions:

The purified Bacillus stearothermophilus threonine deaminase shares regulatory and stability properties with enzymes from mesophilic and thermophilic bacteria.
Environmental factors (pH, temperature) and allosteric effectors (isoleucine, valine) significantly influence enzyme activity, stability, and quaternary structure.