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.

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. 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. 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.

Blood biochemical characteristics, cecal microbiota and short-chain fatty acid composition in fistula implanted rats.

We raised an experimental rat implanted with a cecal fistula and investigated various characteristics of fistula-implanted rats. Male F344/N Sic rats at 14 weeks of age were divided into three groups, the fistula group (n = 5) which consisted of fistula-implanted rats, the sham group (n = 7) which consisted of sham-operated rats, and the control group (n = 7) which were not subjected to any surgical procedure. Four weeks after the fistula implantation surgery, we compared the blood biochemical indices, the microflora composition and the short-chain fatty acids (SCFA) concentration in cecal contents of fistula-implanted rats with those of sham-operated and control rats. The blood albumin concentration of the fistula group was significantly lower than that of the sham group and the control group, and the hematocrit value of the fistula group was significantly lower than that of the control group, but there were no significant differences in the SCFA concentration and the microflora composition among these three groups. In conclusion, it was considered that the fistula-implanted rats are useful for taking cecal contents and determining the microflora composition and the metabolites concentration at any time, without disturbing the physiological functions of the intestinal tract.

Mechanistic study on the roles of a bifidogenetic growth stimulator based on physicochemical characterization.

2-Amino-3-carboxy-1,4-naphthoquinone, discovered as a novel bifidogenetic growth stimulator (BGS), has been characterized by determination of redox and acid-base equilibria, partition properties, and UV-vis and electron spin resonance spectral properties. BGS is proposed to function as an electron transfer mediator from NADH to O2. BGS is reduced by NADH-reduced diaphorase (or related enzymes) and the reduced BGS is reoxidized by autoxidation and a peroxidase-catalyzed reaction. The proposed reaction would spare pyruvate as an important metabolic intermediate, and minimize the cytotoxic effects of H2O2 generated by the autoxidation. Kinetic studies were performed in model enzymatic systems using 2-methyl-1,4-naphthoquinone (VK3) as a reference compound with a very weak growth-stimulating effect. The results support our proposal and reveal the superiority of BGS to VK3 as an electron transfer mediator in the proposed reactions.