A new synthetic route to N-benzyl carboxamides through the reverse reaction of N-substituted formamide deformylase.

Previously, we isolated a new enzyme, N-substituted formamide deformylase, that catalyzes the hydrolysis of N-substituted formamide to the corresponding amine and formate (H. Fukatsu, Y. Hashimoto, M. Goda, H. Higashibata, and M. Kobayashi, Proc. Natl. Acad. Sci. U. S. A. 101:13726-13731, 2004, doi:10.1073/pnas.0405082101). Here, we discovered that this enzyme catalyzed the reverse reaction, synthesizing N-benzylformamide (NBFA) from benzylamine and formate. The reverse reaction proceeded only in the presence of high substrate concentrations. The effects of pH and inhibitors on the reverse reaction were almost the same as those on the forward reaction, suggesting that the forward and reverse reactions are both catalyzed at the same catalytic site. Bisubstrate kinetic analysis using formate and benzylamine and dead-end inhibition studies using a benzylamine analogue, aniline, revealed that the reverse reaction of this enzyme proceeds via an ordered two-substrate, two-product (bi-bi) mechanism in which formate binds first to the enzyme active site, followed by benzylamine binding and the subsequent release of NBFA. To our knowledge, this is the first report of the reverse reaction of an amine-forming deformylase. Surprisingly, analysis of the substrate specificity for acids demonstrated that not only formate, but also acetate and propionate (namely, acids with numbers of carbon atoms ranging from C1 to C3), were active as acid substrates for the reverse reaction. Through this reaction, N-substituted carboxamides, such as NBFA, N-benzylacetamide, and N-benzylpropionamide, were synthesized from benzylamine and the corresponding acid substrates.

Transcriptional regulation of the nitrile hydratase gene cluster in Pseudomonas chlororaphis B23.

An enormous amount of nitrile hydratase (NHase) is inducibly produced by Pseudomonas chlororaphis B23 after addition of methacrylamide as the sole nitrogen source to a medium. The expression pattern of the P. chlororaphis B23 NHase gene cluster in response to addition of methacrylamide to the medium was investigated. Recently, we reported that the NHase gene cluster comprises seven genes (oxdA, amiA, nhpA, nhpB, nhpC, nhpS, and acsA). Sequence analysis of the 1.5-kb region upstream of the oxdA gene revealed the presence of a 936-bp open reading frame (designated nhpR), which should encode a protein with a molecular mass of 35,098. The deduced amino acid sequence of the nhpR product showed similarity to the sequences of transcriptional regulators belonging to the XylS/AraC family. Although the transcription of the eight genes (nhpR, oxdA, amiA, nhpABC, nhpS, and acsA) in the NHase gene cluster was induced significantly in the P. chlororaphis B23 wild-type strain after addition of methacrylamide to the medium, transcription of these genes in the nhpR disruptant was not induced, demonstrating that nhpR codes for a positive transcriptional regulator in the NHase gene cluster. A reverse transcription-PCR experiment revealed that five genes (oxdA, amiA, nhpA, nhpB, and nhpC) are cotranscribed, as are two other genes (nhpS and acsA). The transcription start sites for nhpR, oxdA, nhpA, and nhpS were mapped by primer extension analysis, and putative -12 and -24 sigma(54)-type promoter binding sites were identified. NhpR was found to be the first transcriptional regulator of NHase belonging to the XylS/AraC family.