Journal of Microbiology

Regulation of the Expression of nhaA Gene, Coding Na^+/H^+ Antiporter A of Escherichia coli.: Seo, Sung Yum , Lee, Seung Heon; J. Microbiol. 1995;33(2):120-125.

Abstract: β-galactosidase activity of Escherichia coli cells containing operon fusion nhaA'-'lacZ was monitored to study the regulation of expression of nhaA gene under various conditions. The expression of the fusion was enhanced only by chemicals containing Na^+ or Li^+. This Na^+ or Li^+. This Na^+(Li^+)-specific enhancement of β-galactosidase activity represented the increase in the rate of synthesis of β-galactosidase rather than the decrease in the breakdown rate. The induction pattern was influenced by copy numbers of the gene. Induction by Na^+ or Li^+ was concentration and time dependent, reaching maximum 5-6 fold induction after 2 hours at 0.4-0.5 M for Na^+ or at 0.25-0.35 M for Li^+, Although the expression was induced at much lower concentration of Na^+ at alkaline pH values than at neutral pH in the presence of Na^+, alkaline pH itself did not induced the expression of the fusion in the absence of Na^+. Temperature shift and growth phase of culture did not affect the level of induction.

Characterization of the Two Na^+/H^+ Antiporters of Escherichia coli: Sung-Yum Seo; J. Microbiol. 1998;36(1):9-13.

Abstract: Escherichia coli has two Na^+/H^+ antiporters which can be used to lower intracellular pH transiently elevated upon exposure to alkaline stress and to extrude intracellular Na^+. Previous studies on the propertied of the Na^+/H^+ antiporter were done, but later studies showed that E. coli has two antiporters(Pinner E., Kolter Y., Padan E., Schuldiner S. (1993) J. Biol. Chem 268, 1729~1734). The properties of each antiporter were studied in this report. Both antiporters were specific only to Na^+ and Li^+, and showed hyperbolic kinetics. K_M values of NhaA were 0.8 mM and 2,2mM for Li^+ and Na^+, respectively. K_M values of NhaB were 2.8mM and 12mM for Li^+ and Na^+, respectively. The pH effects can be summarized as follows: 1) both antiporters do not show activity at very acidic pH values; 2) NhaB seems to work in a neutral pH range; 3) NhaA seems to show activity at alkaline pH. The effect of pH on the kinetics of the antiporters was studied. V_max of NhaB remained maximum in the pH range 7.0~8.2. V_max of NhaA increases steeply in the pH range 6.5~7.8 and remained maximum thereafter up to pH 8.6. When the pH was increased, the K_M decreased sharply, especially for NhaA.

Respiratory Chain-Linked Components of the Marine Bacterium Vibrio alginolyticus Affect Each Other: Young Jae Kim; J. Microbiol. 2002;40(2):125-128.

Abstract: The aerobic respiratory chain of Vibrio alginolyticus possesses two different kinds of NADH oxidase systems, i.e., an Na^+ -dependent NADH oxidase system and an Na^+ -independent NADH oxidase system. When deamino-NADH, which is the only substrate for the Na^+ -dependent NADH oxidase system, was used as a substrate, the maximum activities of Na^+ -dependent NADH:quinone oxidoreductase and Na^+ -dependent NADH oxidase were obtained at about 0.06 M and 0.2 M NaCl, respectively. When NADH, which is a substrate for both Na^+ -dependent and Na^+ -independent NADH oxidase systems was used as a substrate, the NADH oxidase activity had a pH optimum at about 8.0. In contrast, when deamino-NADH was used as a substrate, the NADH oxidase activity had a pH optimum at about 9.0. On the other hand, inside-out membrane vesicles prepared from the wild-type bacterium generated only a very small [delta]pH by the NADH oxidase system, whereas inside-out membrane vesicles prepared from Nap1, which is a mutant defective in the Na^+ pump, generated [delta]pH to a considerable extent by the NADH oxidase system. On the basis of the results, it was concluded that the respiratory chain-linked components of V. alginolyticus affect each other.

Cloning of the Gene for Na+/Serine-Threonine Symporter (sstT) from Haemophilus influenzae Rd and Characteristics of the Transporter: Young-Mog Kim; J. Microbiol. 2003;41(3):202-206.

Abstract: A protein, exhibiting a high similarity to the major serine transporter of Escherichia coli, SstT, was found in Haemophilus influenzae Rd. A Na+-stimulated serine transport activity was also detected in the cells. The gene (sstT) for the Na^+/serine symporter from the chromosome of H. influenzae was cloned, and the properties of the transporter investigated. The serine transport activity was stimulated by Na^+. The uptake of Na^+ was elicited by the addition of serine or threonine into the cells, supporting the idea that these amino acids are transported by a mechanism of Na^+/substrate symport. No uptake of H^+ was elicited by the influx of serine. The serine transport via the SstT of H. influenzae was inhibited by excess threonine, which was used as another substrate. The K_m and the V_max values for the serine transport were 2.5 mM and 14 nmol/min/mg protein, respectively.

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