Aromatic aminotransferases in coryneform bacteria.

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• Coryneform bacteria, including Corynebacterium glutamicum, Brevibacterium flavum, and B. ammoniagenes, metabolize aromatic compounds.
• These bacteria possess enzymes capable of transaminating key aromatic pathway intermediates: prephenate, phenylpyruvate, and 4-hydroxy-phenylpyruvate.

Purpose of the Study:

• To characterize the aromatic aminotransferases in C. glutamicum, B. flavum, and B. ammoniagenes.
• To investigate the substrate specificities and properties of these enzymes.
• To explore the potential application of enzyme inhibition for specific metabolic assays.

Main Methods:

• Partial purification of aromatic aminotransferases from bacterial species.
• Determination of molecular weights and substrate specificities of purified enzymes.
• Enzyme activity assays in the presence and absence of pyridoxal-5'-phosphate and phenylhydrazine.

Main Results:

• Two distinct aromatic aminotransferases (I and II) were identified in C. glutamicum and B. flavum, with molecular weights of approximately 155,000 and 260,000, respectively.
• A single aromatic aminotransferase was isolated from B. ammoniagenes.
• Enzymes showed overlapping specificities but differed in substrate preference; pyridoxal-5'-phosphate was tightly bound.
• Phenylhydrazine effectively inhibited aminotransferase activity (90% at 0.1 mM), particularly in B. flavum and C. glutamicum.

Conclusions:

• Coryneform bacteria possess multiple aromatic aminotransferases with distinct molecular properties and substrate preferences.
• The sensitivity of these aminotransferases to phenylhydrazine provides a practical method for selectively inhibiting their activity.
• This selective inhibition facilitates accurate measurement of prephenate dehydratase activity in complex biological samples.