Microbial and plant metabolism of NO

Spatio-temporal expression of phytoglobin: a determining factor in the NO specification of cell fate

Plant growth and development rely on the orchestration of cell proliferation, differentiation, and ultimately death. After varying rounds of divisions, cells respond to positional cues by acquiring a specific fate and embarking upon distinct developmental pathways which might differ significantly from those of adjacent cells exposed to diverse cues. Differential cell behavior is most apparent in response to stress, when some cells might be more vulnerable than others to the same stress condition. This appears to be the case for stem cells which show abnormal features of differentiation and ultimately signs of deterioration at the onset of specific types of stress such as hypoxia and water deficit. A determining factor influencing cell behavior during growth and development, and cell response during conditions of stress is nitric oxide (NO), the level of which can be regulated by phytoglobins (Pgbs), known scavengers of NO. The modulation of NO by Pgbs can be cell, tissue, and/or organ specific, as revealed by the expression patterns of Pgbs dictated by the presence of distinct cis-regulatory elements in their promoters. This review discusses how the temporal and spatial Pgb expression pattern influences NO-mediated responses and ultimately cell fate acquisition in plant developmental processes.

L-Leucine and NO-mediated cardiovascular function

Reduced availability of nitric oxide (NO) in the vasculature is a major factor contributing to the impaired action of insulin on blood flow and, therefore, insulin resistance in obese and diabetic subjects. Available evidence shows that vascular insulin resistance plays an important role in the pathogenesis of cardiovascular disease, the leading cause of death in developed nations. Interestingly, increased concentrations of L-leucine in the plasma occur in obese humans and other animals with vascular dysfunction. Among branched-chain amino acids, L-leucine is unique in inhibiting NO synthesis from L-arginine in endothelial cells and may modulate cardiovascular homeostasis in insulin resistance. Results of recent studies indicate that L-leucine is an activator of glutamine:fructose-6-phosphate aminotransferase (GFAT), which is the first and a rate-controlling enzyme in the synthesis of glucosamine (an inhibitor of endothelial NO synthesis). Through stimulating the mammalian target of rapamycin signaling pathway and thus protein synthesis, L-leucine may enhance GFAT protein expression, thereby inhibiting NO synthesis in endothelial cells. We propose that reducing circulating levels of L-leucine or endothelial GFAT activity may provide a potentially novel strategy for preventing and/or treating cardiovascular disease in obese and diabetic subjects. Such means may include dietary supplementation with either α-ketoglutarate to enhance the catabolism of L-leucine in the small intestine and other tissues or with N-ethyl-L-glutamine to inhibit GFAT activity in endothelial cells. Preventing leucine-induced activation of GFAT by nutritional supplements or pharmaceutical drugs may contribute to improved cardiovascular function by enhancing vascular NO synthesis.

Bioanalytical profile of the L-arginine/nitric oxide pathway and its evaluation by capillary electrophoresis

This review briefly summarizes recent progress in fundamental understanding and analytical profiling of the L-arginine/nitric oxide (NO) pathway. It focuses on key analytical references of NO actions and the experimental acquisition of these references in vivo, with capillary electrophoresis (CE) and high-performance capillary electrophoresis (HPCE) comprising one of the most flexible and technologically promising analytical platform for comprehensive high-resolution profiling of NO-related metabolites. Another aim of this review is to express demands and bridge efforts of experimental biologists, medical professionals and chemical analysis-oriented scientists who strive to understand evolution and physiological roles of NO and to develop analytical methods for use in biology and medicine.

Nitrosyl-heme complexes are formed in the ischemic heart: evidence of nitrite-derived nitric oxide formation, storage, and signaling in post-ischemic tissues

In addition to the generation from specific nitric-oxide (NO) synthases, NO formation from nitrite occurs in ischemic tissues, such as the heart. Although NO binding to heme-centers is the basis for NO-mediated signaling as occurs through guanylate cyclase, it is not known if this process is triggered with physiologically relevant periods of sublethal ischemia and if nitrite serves as a critical substrate. Therefore electron paramagnetic resonance studies were performed to measure nitrosylheme formation during the time course of myocardial ischemia and reperfusion and the role of nitrite in this process. Rat hearts were either partially nitrite-depleted by nitrite-free buffer perfusion or nitrite-enriched by preinfusion with 50 microm nitrite. Ischemic hearts loaded with nitrite showed prominent spectra of six-coordinate nitrosyl-heme complexes, primarily NO-myoglobin, that increased as a function of ischemic duration, whereas in nonischemic-controls these signals were not seen. Total nitrosyl-heme concentrations within the heart were 6.6 +/- 0.7 microm after 30 min of ischemia. Nitrite-depleted hearts also gave rise to NO-heme signals during ischemia, but levels were 8-fold lower. Nitrite-mediated NO-heme complex formation during ischemia was associated with activation of guanylate cyclase. Upon reperfusion, the levels of NO-heme complexes decreased 3-fold by the first 15 min but remained elevated for over 45 min. The decrease in NO-heme complex levels was paralleled by the formation of nitrate, suggesting the oxidation of heme-bound NO upon reperfusion. Thus, nitrite-mediated NO-heme formation occurs progressively during ischemia, with these complexes serving as a store of NO with concordant activation of NO signaling pathways.

A review of the volatile metabolites of fungi found on wood substrates

The holdings of eight collections of fungi have been examined for organisms isolated from wood and/or trees. Further selection of these fungi has been made according to their reported ability to produce volatile, biologically active metabolites. It is emphasized that the isolates in the collections do not necessarily produce such metabolites. The list of fungi fulfilling these conditions is slightly augmented by reports we have found in the literature, where the fungi concerned have not yet been deposited. The biochemistry of these compounds is considered with particular emphasis on their biosynthesis including that by Homo sapiens. The physiological and toxicological activity of these metabolites is reviewed especially with reference to their potential role in the complex symbioses existent in, for example, a tree. The review concludes with a discussion of areas of botany deserving increased attention in the hope that this will stimulate further work. The statements in the review are based on 173 references.

A critical assessment of the neurodestructive and neuroprotective effects of nitric oxide

Whether nitric oxide is cytodestructive or cytoprotective is of obvious clinical importance. The debate on this subject in the past decade has generated much "heat and light". This paper focuses on the actions of NO on the nervous system and reexamines the controversial issue and the contribution of the authors and their colleagues in the light of recent findings. We also report new findings, critically assesses previous experimental data, and share perspectives on this important subject.

Flavorubredoxin, an inducible catalyst for nitric oxide reduction and detoxification in Escherichia coli

Nitric oxide (NO) is a poison, and organisms employ diverse systems to protect against its harmful effects. In Escherichia coli, ygaA encodes a transcription regulator (b2709) controlling anaerobic NO reduction and detoxification. Adjacent to ygaA and oppositely transcribed are ygaK (encoding a flavorubredoxin (flavoRb) (b2710) with a NO-binding non-heme diiron center) and ygbD (encoding a NADH:(flavo)Rb oxidoreductase (b2711)), which function in NO reduction and detoxification. Mutation of either ygaA or ygaK eliminated inducible anaerobic NO metabolism, whereas ygbD disruption partly impaired the activity. NO-sensitive [4Fe-4S] (de)hydratases, including the Krebs cycle aconitase and the Entner-Doudoroff pathway 6-phosphogluconate dehydratase, were more susceptible to inactivation in ygaK or ygaA mutants than in the parental strain, and these metabolic poisonings were associated with conditional growth inhibitions. flavoRb (NO reductase) and flavohemoglobin (NO dioxygenase) maximally metabolized and detoxified NO in anaerobic and aerobic E. coli, respectively, whereas both enzymes scavenged NO under microaerobic conditions. We suggest designation of the ygaA-ygaK-ygbD gene cluster as the norRVW modulon for NO reduction and detoxification.