Vertebrate Acyl CoA synthetase family member 4 (ACSF4-U26) is a β-alanine-activating enzyme homologous to bacterial non-ribosomal peptide synthetase.
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Purified recombinant ACSF4-U26 forms a covalent bond with radiolabelled beta-alanine in an ATP-dependent manner, and the bond is not formed in a point mutant lacking the phosphopantetheine attachment site.
"In the presence of ATP, purified mouse recombinant ACSF4-U26 progressively formed a covalent bond with radiolabelled β-alanine."
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The reaction is almost specific for beta-alanine among the standard amino acids, with a KM of about 5 micromolar.
"Competition experiments with various amino acids indicated that the reaction was almost specific for β-alanine, and a KM of ~ 5 μm was calculated for this reaction."
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Transfer of beta-alanine onto thiols is catalysed by the adenylation domain and does not require the PQQDH-related domain, but was judged physiologically irrelevant; the true acceptor is unidentified and a rare post-translational or post-transcriptional modification is hypothesised.
"suggesting that β-alanine transfer onto thiols is catalysed by the ACSF4-U26 adenylation domain, but is physiologically irrelevant."