2-Amino-3-carboxy-1,4-naphthoquinone

Biochim Biophys Acta. 1999 Aug 5;1428(2-3):241-50.

Role of 2-amino-3-carboxy-1,4-naphthoquinone, a strong growth stimulator for bifidobacteria, as an electron transfer mediator for NAD(P)(+) regeneration in Bifidobacterium longum.[Pubmed: 10434042]

2-Amino-3-carboxy-1,4-naphthoquinone (ACNQ) is a novel growth stimulator for bifidobacteria. The role of ACNQ as a mediator of the electron transfer from NAD(P)H to dioxygen (O(2)) and hydrogen peroxide (H(2)O(2)), proposed in our previous paper, was examined using the cell-free extract and whole cells of Bifidobacterium longum.
METHODS AND RESULTS:
Continuous monitoring of ACNQ, O(2) and H(2)O(2) by several amperometric techniques has revealed that ACNQ works as a good electron acceptor of NAD(P)H diaphorase and that the reduced form of ACNQ is easily autoxidized and also acts as a better electron donor of NAD(P)H peroxidase than NAD(P)H. The generation of H(2)O(2) by B. longum under aerobic conditions is effectively suppressed in the presence of ACNQ. These ACNQ-mediated reactions would play roles as NAD(P)(+)-regeneration processes. The accumulation of ACNQ in the cytosol has been also suggested. These characteristics of ACNQ seem to be responsible for the growth stimulation of bifidobacteria.
CONCLUSIONS:
Vitamin K(3), which has an extremely low growth-stimulating activity and was used as a reference compound, exhibits much lower activity as an electron transfer mediator. The difference in the activity is discussed in terms of the redox potential and partition property of the quinones.

Appl Microbiol Biotechnol. 2002 Jun;59(1):72-8.

2-Amino-3-carboxy-1,4-naphthoquinone affects the end-product profile of bifidobacteria through the mediated oxidation of NAD(P)H.[Pubmed: 12073135 ]

Glucose metabolism of bifidobacteria in the presence of 2-Amino-3-carboxy-1,4-naphthoquinone (ACNQ), a specific growth stimulator for bifidobacteria, and ferricyanide (Fe(CN)(6)(3-)) as an extracellular electron acceptor was examined using resting cells of Bifidobacterium longum and Bifidobacterium breve.
METHODS AND RESULTS:
NAD(P)H in the cells is oxidized by ACNQ with the aid of diaphorase activity, and reduced ACNQ donates the electron to Fe(CN)(6)(3-). Exogenous oxidation of NADH by the ACNQ/Fe(CN)(6)(3-) system suppresses the endogenous lactate dehydrogenase reaction competitively, which results in the remarkable generation of pyruvate and a decrease in lactate production. In addition, a decrease in acetate generation is also observed in the presence of ACNQ and Fe(CN)(6)(3-). This phenomenon could not be explained in terms of the fructose-6-phosphate phosphoketolase pathway, but suggests rather that glucose is partially metabolized via the hexose monophosphate pathway. This was verified by NADP(+)-induced reduction of Fe(CN)(6)(3-) in cell-free extracts in the presence of ACNQ. Effects of the ACNQ/Fe(CN)(6)(3-) system on anaerobically harvested cells were also examined.
CONCLUSIONS:
Stoichiometric analysis of the metabolites from the pyruvate-formate lyase pathway suggests that exogenous oxidation of NADH is an efficient method to produce ATP in this pathway.