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

2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) is a growth stimulator for bifidobacteria that is excreted by propionic acid bacteria ^[1,2,3].

2-amino-3-carboxy-1,4-naphthoquinone is produced and excreted by Propionibacterium freundenreichii, and plays a role as an electron transfer mediator from NAD(P)H to oxygen and hydrogen peroxide in the cytoplasm of the obligate naerobe Bifidobacterium longum. B. longum does not have a respiratory chain and normally regenerates NAD(P)+ by a lactate dehydrogenase-catalyzed reaction, consuming pyruvate and excreting lactate. This process consumes an important intracellular metabolite (e.g., pyruvate), and becomes thermodynamically unfavorable if actate accumulates in the environment. 2-amino-3-carboxy-1,4-naphthoquinone offers an alternative pathway catalyzed by cytosolic diaphorase and peroxidase. By coupling the regeneration of NAD(P)+ to the reduction of O2 and H2O2, 2-amino-3-carboxy-1,4-naphthoquinone stimulates growth and is thought to protect B. longum from oxygen toxicity. The hydrophilicity of 2-amino-3-carboxy-1,4-naphthoquinone increases upon reduction, promoting its accumulation inside the cell. Therefore, only very low concentrations of extracellular ACNQ (i.e., 0.5 nM) are required for it to stimulate the growth of B. longum ^[4].

References:
[1]. Yamazaki S, Kaneko T, Taketomo N, et al. Glucose metabolism of lactic acid bacteria changed by quinone-mediated extracellular electron transfer[J]. Bioscience, biotechnology, and biochemistry, 2002, 66(10): 2100-2106.
[2]. Yamazaki S, Kano K, Ikeda T, et al. 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[J]. Biochimica et Biophysica Acta (BBA)-General Subjects, 1999, 1428(2-3): 241-250.
[3]. Mori H, Sato Y, Taketomo N, et al. Isolation and structural identification of bifidogenic growth stimulator produced by Propionibacterium freudenreichii[J]. Journal of Dairy Science, 1997, 80(9): 1959-1964.
[4]. Hernandez M E, Newman D K. Extracellular electron transfer[J]. Cellular and Molecular Life Sciences CMLS, 2001, 58(11): 1562-1571.

2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) 是双歧杆菌的生长刺激剂，由丙酸细菌 ^[1,2,3] 分泌。

2-amino-3-carboxy-1,4-naphthoquinone 由 Propionibacterium freundenreichii 产生和分泌，在专性细胞的细胞质中充当从 NAD(P)H 到氧和过氧化氢的电子转移介质厌氧菌长双歧杆菌。 B. longum 没有呼吸链，通常通过乳酸脱氢酶催化的反应再生 NAD(P)+，消耗丙酮酸并排出乳酸。该过程消耗重要的细胞内代谢物（例如丙酮酸），如果乙酸在环境中积累，则在热力学上变得不利。 2-amino-3-carboxy-1,4-naphthoquinone 提供了一种由胞质心肌黄酶和过氧化物酶催化的替代途径。通过将 NAD(P)+ 的再生与 O2 和 H2O2 的还原相结合，2-amino-3-carboxy-1,4-naphthoquinone 可刺激生长，并被认为可以保护长双歧杆菌免受氧中毒。 2-amino-3-carboxy-1,4-naphthoquinone 的亲水性在还原时增加，促进其在细胞内的积累。因此，仅需极低浓度的胞外ACNQ（即0.5 nM）即可刺激长双歧杆菌^[4]的生长。