A novel bifunctional aspartate kinase-homoserine dehydrogenase from the hyperthermophilic bacterium, Thermotoga maritima

The capacity of three maize endosperm opaque mutants (o10, o11 and o13) to accumulate soluble lysine in the seed in relation to their wildtype counterpart, W22+, was investigated. The W22o13 and W22o11 mutants exhibited 278% and 186% increases in soluble lysine, respectively, while for W22o10, a 36% decrease was observed, compared with the wildtype. A quantitative and qualitative study of the N constituents of the endosperm has been conducted and data obtained for the total protein, non-protein N, soluble amino acids, albumins / globulins, zeins and glutelins present in the seed of the mutants. Following 2D–PAGE, a total of 38 different forms of zein polypeptides were detected and considerable differences were noted between the three mutant lines. The metabolism of lysine was also studied by analysis of the enzymes aspartate kinase, homoserine dehydrogenase, lysine 2-oxoglutarate reductase and saccharopine dehydrogenase, which exhibited major changes in activity, depending on the genotype, suggesting that the mutant genes may have distinct regulatory activities.

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Expression and Characterization of a Novel Nitrilase from Hyperthermophilic Bacterium Thermotoga maritima MSB8

Journal of Microbiology and Biotechnology ◽

10.4014/jmb.1502.02032 ◽

2015 ◽

Vol 25 (10) ◽

pp. 1660-1669 ◽

Cited By ~ 4

Author(s):

Zhi Chen ◽

Huayou Chen ◽

Zhong Ni ◽

Rui Tian ◽

Tianxi Zhang ◽

...

Keyword(s):

Thermotoga Maritima ◽

Hyperthermophilic Bacterium

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Cellular Amino Acid Concentrations and Regulation of Aspartate Kinase in the Thermophilic Phototrophic Prokaryote Chloroflexus aurantiacus

Zeitschrift für Naturforschung C ◽

10.1515/znc-1990-1-213 ◽

1990 ◽

Vol 45 (1-2) ◽

pp. 74-78 ◽

Cited By ~ 2

Author(s):

Jobst-Heinrich Klemme ◽

Gisela Laakmann-Ditges ◽

Jutta Mertschuweit

Keyword(s):

Amino Acid ◽

Feedback Inhibition ◽

Gel Filtration ◽

Break Point ◽

Test System ◽

Chloroflexus Aurantiacus ◽

Aspartate Kinase ◽

Homoserine Dehydrogenase ◽

Molecular Weights ◽

Amino Acid Concentrations

Aspartate kinase (AK , EC 2.7.2.4) from the thermophilic, phototrophic prokaryote, Chloroflexus aurantiacus, was partially purified and separated from homoserine dehydrogenase (HSDH, EC 1.1.1.3). The molecular weights as determined by gel filtration were 130,000 and 46,000, respectively. HSDH had a moderately high thermal stability (50% inactivation at 84 °C) and displayed its activity optimum at 72 °C. By contrast, AK had its activity optimum at 52 °C (with a break-point in the Arrhenius plot at 42 °C) and was much less thermostable (50% inactivation at 67 °C). The Km-values for aspartate and ATP (determined in a pyruvate kinase-coupled test system) were 10.5 and 0.63 mM , respectively. The enzyme was strongly inhibited by L-threonine (Ki = 10 μm) and activated by alanine, isoleucine, valine and methionine. L-Threonine acted as a mixed-type inhibitor in respect to aspartate, and non-competitively in respect to ATP. Contrary to AKs from Rhodospirillaceae, the enzyme from Chloroflexus aurantiacus was not subject to a concerted feedback inhibition by two amino acids of the aspartate family. The regulatory properties of the aspartate kinase are discussed in relation to the cellular amino acid concentrations.

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