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The biochemical basis for growth inhibition by L-phenylalanine in Neisseria gonorrhoeae
R K Bhatnagar1, A Berry, A T Hendry
1Department of Microbiology and Cell Science, University of Florida, Gainesville 32611.
Abstract:
Clinical isolates of Neisseria gonorrhoeae are commonly subject to growth inhibition by phenylpyruvate or by L-phenylalanine. A blockade of tyrosine biosynthesis is indicated since inhibition is reversed by either L-tyrosine or 4-hydroxyphenylpyruvate. Phenylalanine-resistant (PheR) and phenylalanine-sensitive (PheS) isolates both have a single 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase that is partially inhibited by L-phenylalanine (80%). However, PheS and PheR isolates differ in that the ratio of phenylpyruvate aminotransferase to 4-hydroxyphenylpyruvate aminotransferase is distinctly greater in PheS isolates than in PheR isolates. A mechanism for growth inhibition is proposed in which phenylalanine exerts two interactive effects. (i) Phenylalanine decreases precursor flow to 4-hydroxyphenylpyruvate through its controlling effect upon DAHP synthase; and (ii) phenylalanine is largely transaminated to phenylpyruvate, which saturates both aminotransferases, preventing transamination of an already limited supply of 4-hydroxyphenylpyruvate to L-tyrosine.
Insights
Neisseria gonorrhoeae growth is inhibited by L-phenylalanine, which blocks tyrosine biosynthesis. This occurs because L-phenylalanine limits precursors and is converted to phenylpyruvate, preventing essential L-tyrosine production.
Area of Science:
- Microbiology
- Biochemistry
Background:
- Neisseria gonorrhoeae clinical isolates exhibit growth inhibition by phenylpyruvate and L-phenylalanine.
- This inhibition is reversible by L-tyrosine or 4-hydroxyphenylpyruvate, suggesting a blockade in tyrosine biosynthesis.
Purpose of the Study:
- To elucidate the mechanism of L-phenylalanine-induced growth inhibition in Neisseria gonorrhoeae.
- To differentiate the roles of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase and aminotransferases in phenylalanine sensitivity.
Main Methods:
- Comparative analysis of phenylalanine-resistant (PheR) and phenylalanine-sensitive (PheS) isolates.
- Enzyme activity assays for DAHP synthase and aminotransferases (phenylpyruvate and 4-hydroxyphenylpyruvate aminotransferase).
Main Results:
- Both PheR and PheS isolates possess a single DAHP synthase partially inhibited by L-phenylalanine.
- PheS isolates exhibit a higher ratio of phenylpyruvate aminotransferase to 4-hydroxyphenylpyruvate aminotransferase compared to PheR isolates.
- L-phenylalanine inhibits DAHP synthase, reducing precursor flow, and is transaminated to phenylpyruvate, saturating aminotransferases and blocking tyrosine synthesis.
Conclusions:
- L-phenylalanine inhibits Neisseria gonorrhoeae growth through a dual mechanism involving precursor limitation and impaired tyrosine synthesis.
- Differential aminotransferase activity contributes to varying sensitivities to L-phenylalanine among clinical isolates.