Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Denitrification and methylotrophy in Paracoccus denitrificans are discussed. The properties of the enzymes of denitrification: the nitrate-nitrite antiporter, nitrate reductase, nitrite reductase, nitric oxide reductase and nitrous oxide reductase are described. The genes for none of these proteins have yet been cloned and sequenced from P. denitrificans. A number of sequences are available for enzymes from Escherichia coli, Pseudomonas stutzeri and Pseudomonas aeruginosa. It is concluded that pathway specific c-type cytochromes are involved in denitrification. At least 40 genes are involved in denitrification. In methanol oxidation at least 20 genes are involved. In this case too pathway specific c-type cytochromes are involved. The sequence homology between the quinoproteins methanol dehydrogenase, alcoholde-hydrogenase and glucose dehydrogenase is discussed. This superfamily of proteins is believed to be derived from a common ancestor. The moxFJGI operon determines the structural components of methanol dehydrogenase and the associated c-type cytochrome. Upstream of this operon 3 regulatory proteins were found. The moxY protein shows the general features of a sensor protein and the moxX protein those of a regulatory protein. Thus a two component regulatory system is involved in both denitrification and methylotrophy. The phylogeny of prokaryotes based on 16S rRNA sequence is discussed. It is remarkable that the 16S rRNA of Thiosphaera pantotropha is identical to that of P. denitrificans. Still these bacteria show a number of differences. T. pantotropha is able to denitrify under aerobic circumstances and it shows heterotrophic nitrification. Nitrification and heterotrophic nitrification are found in species belonging to the beta-and gamma-subdivisions of purple non-sulfur bacteria. Thus the occurrence of heterotrophic nitrification in T. pantotropha, which belongs to the alpha-subdivision of purple non-sulfur bacteria is a remarkable property. Furthermore T. pantotropha contains two nitrate reductases of which the periplasmic one is supposed to be involved in aerobic denitrification. The nitrite reductase is of the Cu-type and not of the cytochrome cd1 type as in P. denitrificans. Also the cytochrome b of the Qbc complex of T. pantotropha is highly similar to its counterpart in P. denitrificans. It is hypothesized that the differences between these two organisms which both contain large megaplasmids is due to a combination of loss of genetic information and plasmid-coded properties. The distribution of a number of complex metabolic systems in eubacteria and in a number of species belonging to the alpha-group of purple non sulphur bacteria is reviewed.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Metabolic pathways in Paracoccus denitrificans and closely related bacteria in relation to the phylogeny of prokaryotes. 157 65

As with all organisms, plants must respond to a plethora of external environmental cues. Individual plant cells must also perceive and respond to a wide range of internal signals. It is now well-accepted that nitric oxide (NO) is a component of the repertoire of signals that a plant uses to both thrive and survive. Recent experimental data have shown, or at least implicated, the involvement of NO in reproductive processes, control of development and in the regulation of physiological responses such as stomatal closure. However, although studies concerning NO synthesis and signalling in animals are well-advanced, in plants there are still fundamental questions concerning how NO is produced and used that need to be answered. For example, there is a range of potential NO-generating enzymes in plants, but no obvious plant nitric oxide synthase (NOS) homolog has yet been identified. Some studies have shown the importance of NOS-like enzymes in mediating NO responses in plants, while other studies suggest that the enzyme nitrate reductase (NR) is more important. Still, more published work suggests the involvement of completely different enzymes in plant NO synthesis. Similarly, it is not always clear how NO mediates its responses. Although it appears that in plants, as in animals, NO can lead to an increase in the signal cGMP which leads to altered ion channel activity and gene expression, it is not understood how this actually occurs. NO is a relatively reactive compound, and it is not always easy to study. Furthermore, its biological activity needs to be considered in conjunction with that of other compounds such as reactive oxygen species (ROS) which can have a profound effect on both its accumulation and function. In this paper, we will review the present understanding of how NO is produced in plants, how it is removed when its signal is no longer required and how it may be both perceived and acted upon.
 ...
PMID:Nitric oxide synthesis and signalling in plants. 1803 72