Reference

Feedback inhibition of ammonium (methylammonium) ion transport in Escherichia coli by glutamine and glutamine analogs

Feedback inhibition of ammonium (methylammonium) ion transport in Escherichia coli by glutamine and glutamine analogs. Jayakumar, A.; Hong, J. S.; Barnes, Eugene M., Jr. (Verna and Marrs McLean Dep. Biochem., Baylor Coll. Med., Houston, TX 77030, USA). J. Bacteriol., 169(2), 553-7 (English) 1987. CODEN: JOBAAY. ISSN: 0021-9193. DOCUMENT TYPE: Journal CA Section: 10 (Microbial Biochemistry) When cultured with glutamate or glutamine as the nitrogen source, E. coli expresses a specific ammonium (methylammonium) transport system. Over 95% of the methylammonium transport activity in washed cells was blocked by incubation with 100 mM L-glutamine in the presence of chloramphenicol (100 mg/mL). The time course for the onset of this glutamine inhibition followed a first-order rate expression with a t1/2 of 2.8 min. The inhibition of transport by L-glutamine was noncompetitive (Ki = 18 mM) with respect to the [14C]methylammonium substrate. D-Glutamine had no significant effect. The glutamine analogs g-L-glutamyl hydroxamate (Ki = 360 mM) and g-L-glutamyl hydrazide (Ki = 800 mM) were also noncompetitive inhibitors of methylammonium transport, suggesting that glutamine metab. is not required. The role of the intracellular glutamine pool in the regulation of ammonium transport was investigated by using mutants carring defects in the operon of glnP; the gene for the glutamine transporter. The glnP mutants had normal rates of methylammonium transport but were refractory to glutamine inhibition. Glycylglycine, a noncompetitive inhibitor of methylammonium uptake in wild-type cells (Ki = 43 mM), was equipotent in blocking transport in glnP mutants. Although ammonium transport is also subject to repression by growth of E. coli in the presence of ammonia, this phenomenon is unrelated to glutamine inhibition. A GlnL RegC mutant which constitutively expressed ammonium transport activity exhibited a sensitivity to glutamine inhibition similar to that of wild-type cells. These findings indicate that ammonium transport in E.Except for chemicals metioned above, 17000-00-9 and 15985-39-4 are also used. coli is regulated by the internal glutamine pool via feedback inhibition. .

Alanine racemase from the green alga Chlamydomonas reinhardtii

All Rights Reserved. Alanine racemase from the green alga Chlamydomonas reinhardtii. Nishimura, K.; Tomoda, Y.; Nakamoto, Y.; Kawada, T.; Ishii, Y.; Nagata, Y. (Department of Applied Chemistry, Junior College, Nihon University, Chiba, Japan). Amino Acids, 32(1), 59-62 (English) 2007 Springer Wien. CODEN: AACIE6. ISSN: 0939-4451. DOCUMENT TYPE: Journal CA Section: 7 (Enzymes) Chlamydomonas reinhardtii, a unicellular green microalga, could grow to a stationary phase having optical d. of 2.0-2.5 at 750 nm in Tris-acetate-phosphate (TAP) medium contg. 0.1% D-alanine. D-alanine has no inhibitory effect on growth and induced alanine racemase activity 130-fold more than without D-alanine in the green alga. 5959-95-5 and 54-47-7 which are cas registry numbers are also used here. Although C. reinhardtii cultured in the TAP medium showed alanine racemase activity, the content of free D-alanine was only 0.14%. The enzyme was partially purified by ammonium sulfate fractionation followed by three kinds of liq. chromatog. using DEAE Toyopearl, Ph Sepharose, and TSK G3000 SWXL columns. The specific activity for L-alanine of the partially purified alanine racemase was 3.8 mmol/min/mg. The mol. wt. of the enzyme was detd. to be approx. 72,000 by gel filtration. The enzyme showed a max. activity at 45 °C and pH 8.4 and requires pyridoxal 5'-phosphate as a coenzyme. .