Bioconversion of 2-amino acids to 2-hydroxy acids byClostridium butyricum

Abstract

Analysis by gas chromatography‐mass spectrometry (GC‐MS) of 24‐h cultures of Clostridium butyricum type strain in synthetic BMG medium supplemented with various 2‐amino acids (10 mM) revealed the presence of the corresponding 2‐hydroxy acids. C. butyricum was able to bioconvert l‐valine, dl‐norvaline, l‐leucine, dl‐norleucine, l‐methionine and l‐phenylalanine as well as unusual 2‐amino acids, i.e., l‐2‐aminobutyric acid, l‐2‐amino‐4‐pentenoic acid, dl‐2‐aminooctanoic acid, and dl‐2‐amino‐4‐phenylbutanoic acid. l‐Isoleucine and cycloleucine were not converted into their corresponding 2‐hydroxy acids. The bioconversion rate was maximal with dl‐norvaline (6.2%). Chiral GC analysis demonstrated that only d‐2‐hydroxy‐4‐methylpentanoic acid is formed from l‐leucine, indicating that the bioconversion is stereospecific, with inversion of configuration. d‐Leucine and d‐methionine were also converted to the corresponding 2‐hydroxy acids. This observation opens new aspects in the study of C. butyricum and raises questions about the amino acid metabolism by this species.

Relationship between Protein Expression Pattern and Host Metabolome Perturbation as Monitored by Two‐Dimensional NMR Spectroscopy

“…The 2‐hydroxy‐3‐methylbutanoic acid is one of the degradation products of the branched‐chain amino acids (BCAAs) in Clostridium butyricum . Its accumulation would mean that the hydrophobic amino acids were being recycled, which in turn would mean that such amino acids could contribute to aggregation of the target protein, probably by binding to its hydrophobic surface or the core, making it more unstable to remain in a soluble form.…”