非表示:
キーワード:
-
要旨:
Aromatic amines like 2-phenylethylamine (2-PEA) and benzylamine (BAm)
have been identified as novel growth substrates of the
betaproteobacterium Aromatoleurn aromaticum EbN1, which degrades a wide
variety of aromatic compounds in the absence of oxygen under
denitrifying growth conditions. The catabolic pathway of these amines
was identified, starting with their oxidative deamination to the
corresponding aldehydes, which are then further degraded via the enzymes
of the phenylalanine or benzyl alcohol metabolic pathways. Two different
periplasmic quinohemoprotein amine dehydrogenases involved in 2-PEA or
BAm metabolism were identified and characterized. Both enzymes consist
of three subunits, contain two heme c cofactors in their alpha-subunits,
and exhibit extensive processing of their gamma-subunits, generating
four intramolecular thioether bonds and a cysteine tryptophylquinone
(CTQ) cofactor. One of the enzymes was present in cells grown with 2-PEA
or other substrates, showed an alpha(2)beta(2)gamma(2) composition, and
had a rather broad substrate spectrum, which included 2-PEA, BAm,
tyramine, and 1-butylamine. In contrast, the other enzyme was
specifically induced in BAm-grown cells, showing an alpha beta gamma
composition and activity only with BAm and 2-PEA. Since the former
enzyme showed the highest catalytic efficiency with 2-PEA and the latter
with BAm, they were designated 2-PEADH and benzylamine dehydrogenase
(BAmDH). The catalytic properties and inhibition patterns of 2-PEADH and
BAmDH showed considerable differences and were compared to previously
characterized quinohemoproteins of the same enzyme family.
IMPORTANCE The known substrate spectrum of A. aromaticum EbN1 is
expanded toward aromatic amines, which are metabolized as sole
substrates coupled to denitrification. The characterization of the two
quinohemoprotein isoenzymes involved in degrading either 2-PEA or BAm
expands the knowledge of this enzyme family and establishes for the
first time that the necessary maturation of their quinoid CTQ cofactors
does not require the presence of molecular oxygen. Moreover, the study
revealed a highly interesting regulatory phenomenon, suggesting that
growth with BAm leads to a complete replacement of 2-PEADH by BAmDH,
which has considerably different catalytic and inhibition properties.
