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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prochlorococcus is one of the dominant cyanobacteria and a key primary producer in oligotrophic intertropical oceans. Here we present an overview of the pathways of nitrogen assimilation in Prochlorococcus, which have been significantly modified in these microorganisms for adaptation to the natural limitations of their habitats, leading to the appearance of different ecotypes lacking key enzymes, such as nitrate reductase, nitrite reductase, or urease, and to the simplification of the metabolic regulation systems. The only nitrogen source utilizable by all studied isolates is ammonia, which is incorporated into glutamate by glutamine synthetase. However, this enzyme shows unusual regulatory features, although its structural and kinetic features are unchanged. Similarly, urease activities remain fairly constant under different conditions. The signal transduction protein P(II) is apparently not phosphorylated in Prochlorococcus, despite its conserved amino acid sequence. The genes amt1 and ntcA (coding for an ammonium transporter and a global nitrogen regulator, respectively) show noncorrelated expression in Prochlorococcus under nitrogen stress; furthermore, high rates of organic nitrogen uptake have been observed. All of these unusual features could provide a physiological basis for the predominance of Prochlorococcus over Synechococcus in oligotrophic oceans.
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PMID:Streamlined regulation and gene loss as adaptive mechanisms in Prochlorococcus for optimized nitrogen utilization in oligotrophic environments. 1559 Jul 77

Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N(2), and some cyanobacteria can also assimilate arginine or glutamine. ABC (ATP-binding cassette)-type permeases are involved in the uptake of nitrate/nitrite, urea and most amino acids, whereas secondary transporters take up ammonium and, in some strains, nitrate/nitrite. In cyanobacteria, nitrate and nitrite reductases are ferredoxin-dependent enzymes, arginine is catabolized by a combination of the urea cycle and arginase pathway, and urea is degraded by a Ni(2+)-dependent urease. These pathways provide ammonium that is incorporated into carbon skeletons through the glutamine synthetase-glutamate synthase cycle, in which 2-oxoglutarate is the final nitrogen acceptor. The expression of many nitrogen assimilation genes is subjected to regulation being activated by the nitrogen-control transcription factor NtcA, which is autoregulatory and whose activity appears to be influenced by 2-oxoglutarate and the signal transduction protein P(II). In some filamentous cyanobacteria, N(2) fixation takes place in specialized cells called heterocysts that differentiate from vegetative cells in a process strictly controlled by NtcA.
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PMID:Nitrogen assimilation and nitrogen control in cyanobacteria. 1566 95

Knowledge about nitrogen metabolism and control in the genus Mycobacterium is sparse, especially compared to the state of knowledge in related actinomycetes like Streptomyces coelicolor or the close relative Corynebacterium glutamicum. Therefore, we screened the published genome sequences of Mycobacterium smegmatis, Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium avium ssp. paratuberculosis and Mycobacterium leprae for genes encoding proteins for uptake of nitrogen sources, nitrogen assimilation and nitrogen control systems, resulting in a detailed comparative genomic analysis of nitrogen metabolism-related genes for all completely sequenced members of the genus. Transporters for ammonium, nitrate, and urea could be identified, as well as enzymes crucial for assimilation of these nitrogen sources, i.e. glutamine synthetase, glutamate dehydrogenase, glutamate synthase, nitrate reductase, nitrite reductase, and urease proteins. A reduction of genes encoding proteins for nitrogen transport and metabolism was observed for the pathogenic mycobacteria, especially for M. leprae. Signal transduction components identified for the different species include adenylyl- and uridylyltransferase and a P(II)-type signal transduction protein. Exclusively for M. smegmatis, two homologs of putative nitrogen regulatory proteins were found, namely GlnR and AmtR, while in other mycobacteria, AmtR was absent and GlnR seems to be the nitrogen transcription regulator protein.
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PMID:A genomic view on nitrogen metabolism and nitrogen control in mycobacteria. 1882 37

PII signal transduction proteins are widely spread among all domains of life where they regulate a multitude of carbon and nitrogen metabolism related processes. Non-diazotrophic cyanobacteria can utilize a high variety of organic and inorganic nitrogen sources. In recent years, several physiological studies indicated an involvement of the cyanobacterial PII protein in regulation of ammonium, nitrate/nitrite, and cyanate uptake. However, direct interaction of PII has not been demonstrated so far. In this study, we used biochemical, molecular genetic and physiological approaches to demonstrate that PII regulates all relevant nitrogen uptake systems in Synechocystis sp. strain PCC 6803: PII controls ammonium uptake by interacting with the Amt1 ammonium permease, probably similar to the known regulation of E. coli ammonium permease AmtB by the PII homolog GlnK. We could further clarify that PII mediates the ammonium- and dark-induced inhibition of nitrate uptake by interacting with the NrtC and NrtD subunits of the nitrate/nitrite transporter NrtABCD. We further identified the ABC-type urea transporter UrtABCDE as novel PII target. PII interacts with the UrtE subunit without involving the standard interaction surface of PII interactions. The deregulation of urea uptake in a PII deletion mutant causes ammonium excretion when urea is provided as nitrogen source. Furthermore, the urea hydrolyzing urease enzyme complex appears to be coupled to urea uptake. Overall, this study underlines the great importance of the PII signal transduction protein in the regulation of nitrogen utilization in cyanobacteria.
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PMID:The Signal Transduction Protein PII Controls Ammonium, Nitrate and Urea Uptake in Cyanobacteria. 3129 55