Subunit structure of biodegradative threonine deaminase

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Biodegradative threonine deaminase is a key enzyme in microbial metabolism.
• Understanding enzyme structure is crucial for elucidating function and regulation.

Purpose of the Study:

• To determine the molecular weight and subunit composition of Escherichia coli biodegradative threonine deaminase.
• To identify the N-terminal and C-terminal amino acid residues of the enzyme.

Main Methods:

• Sedimentation equilibrium ultracentrifugation was used to determine the native molecular weight.
• Sodium dodecyl sulfate-gel electrophoresis and guanidinium chloride treatment were employed to assess subunit size.
• N-terminal sequencing via dinitrophenylation and automated sequence analysis, along with C-terminal analysis using selective tritium labeling, were performed.

Main Results:

• The native enzyme's molecular weight was determined to be approximately 147,000 g/mol.
• The enzyme dissociated into subunits with molecular weights of approximately 39,000-38,000 g/mol under denaturing conditions.
• Methionine was identified as the N-terminal residue, with 3.6 moles per 147,000 g of enzyme.
• Alanine was identified as the C-terminal residue.
• Automated sequencing indicated identical amino acid sequences among the subunits.

Conclusions:

• The native Escherichia coli biodegradative threonine deaminase is a tetramer, composed of four identical polypeptide subunits.
• The enzyme's quaternary structure is formed by homologous subunits, each with the same amino acid sequence.