Uric acid-dependent inhibition of AMP kinase induces hepatic glucose production in diabetes and starvation: evolutionary implications of the uricase loss in hominids.

Reduced AMP kinase (AMPK) activity has been shown to play a key deleterious role in increased hepatic gluconeogenesis in diabetes, but the mechanism whereby this occurs remains unclear. In this article, we document that another AMP-dependent enzyme, AMP deaminase (AMPD) is activated in the liver of diabetic mice, which parallels with a significant reduction in AMPK activity and a significant increase in intracellular glucose accumulation in human HepG2 cells. AMPD activation is induced by a reduction in intracellular phosphate levels, which is characteristic of insulin resistance and diabetic states. Increased gluconeogenesis is mediated by reduced TORC2 phosphorylation at Ser171 by AMPK in these cells, as well as by the up-regulation of the rate-limiting enzymes PEPCK and G6Pc. The mechanism whereby AMPD controls AMPK activation depends on the production of a specific AMP downstream metabolite through AMPD, uric acid. In this regard, humans have higher uric acid levels than most mammals due to a mutation in uricase, the enzyme involved in uric acid degradation in most mammals, that developed during a period of famine in Europe 1.5 × 10(7) yr ago. Here, working with resurrected ancestral uricases obtained from early hominids, we show that their expression on HepG2 cells is enough to blunt gluconeogenesis in parallel with an up-regulation of AMPK activity. These studies identify a key role AMPD and uric acid in mediating hepatic gluconeogenesis in the diabetic state, via a mechanism involving AMPK down-regulation and overexpression of PEPCK and G6Pc. The uricase mutation in the Miocene likely provided a survival advantage to help maintain glucose levels under conditions of near starvation, but today likely has a role in the pathogenesis of diabetes.

AMP deaminase 3 plays a critical role in remote reperfusion lung injury.

Remote reperfusion lung injury following skeletal muscle ischemia and reperfusion accounts for high morbidity and mortality. AMP deaminase (AMPD), a key enzyme for nucleotide cycle, has been implicated in the regulation of this phenomenon. However, the function of Ampd2 and Ampd3 subtype has not been elucidated in remote reperfusion rodent lung injury. We utilized AMPD3 and AMPD2-deficient mice. The two types of AMPD-deficient mice and wild-type (WT) littermates were subjected to ischemia-reperfusion injury. After 3h bilateral hind-limb ischemia and reperfusion, AMPD3 mRNA, AMPD activity and inosine monophosphate (IMP) increased significantly in WT and AMPD2-deficient mice lungs, while they did not show significant alterations in AMPD3-deficient mice lungs. Genetic inactivation of Ampd3 resulted in markedly accelerated myeloperoxidase (MPO) activity along with exaggerated neutrophils infiltration and hemorrhage in the lungs compared to WT and AMPD2-deficient mice, furthermore, IMP treatment significantly attenuated MPO activity and neutrophils infiltration in WT and the two types of AMPD-deficient mice lungs after 3h reperfusion. These findings demonstrate for the first time in AMP-deficient mice models that AMPD3 plays a critical role in remote reperfusion lung injury via generation of IMP and validate the potential to use IMP into the clinical arena to attenuate remote ischemia-reperfusion lung injury.

[AMPD genes and urate metabolism].

AMPD (AMP deaminase), an enzyme catalyzing AMP to IMP, plays an important role in purine/urate metabolism. AMPD is encoded in 3 genes for 3 isozymes M, L and E (H), respectively. In humans, 2 AMPD deficiencies have been reported in skeletal muscles (AMPD1 deficiency) and red blood cells (AMPD3 deficiency). AMPD1 deficiency has been found in patients with metabolic myopathy. AMPD regulates important purine nucleotides including ATP, ADP, AMP, IMP et al. Also, AMPD deficiency may change the level of adenosine, an important bioactive molecule. In addition, AMP activated protein kinase (AMPK) activity, controlled by intracellular AMP, has an important role as an energy sensor. Therefore, AMPD may control the systemic metabolic status by changing AMPK activity through the AMP level.

Remote reperfusion lung injury is associated with AMP deaminase 3 activation and attenuated by inosine monophosphate.

BACKGROUND: Remote reperfusion lung injury occurs in patients with vascular occlusion and surgical procedures. Inosine monophosphate (IMP) produced by adenosine monophosphate deaminase (AMPD) 3 is involved in the remote reperfusion injury. The purpose of the present study was to identify whether IMP administration attenuated the remote reperfusion lung injury in a skeletal muscle ischemia-reperfusion model. METHODS AND RESULTS: A remote reperfusion lung injury was created using reperfusion after the bilateral ligation of the hind-limb. AMPD activity, myeloperoxidase (MPO) activity, IMP, AMPD3 mRNA and tumor necrosis factor (TNF)-alpha in the lungs before and after reperfusion were analyzed. Furthermore, the effects of IMP on these parameters were examined. AMPD3 mRNA, AMPD activity and IMP production in the lungs significantly increased after ischemia-reperfusion with increases in MPO activity, TNF-alpha level and decreased oxygen saturation (SpO(2)). Histological examination of the lungs demonstrated significant neutrophil infiltration and accumulation. IMP administration significantly reduced MPO activity, TNF-alpha and neutrophil infiltration, with ameliorated SpO(2). CONCLUSIONS: Along with the activation of AMPD3, ischemia-reperfusion-induced lung inflammation is associated with increased MPO activity and TNF-alpha level. IMP significantly decreased the lung injury, MPO activity, TNF-alpha and increased SpO(2). These findings may lead to the development of a new therapeutic strategy for remote reperfusion lung injury.

Membrane association, mechanism of action, and structure of Arabidopsis embryonic factor 1 (FAC1).

Embryonic factor 1 (FAC1) is one of the earliest expressed plant genes and encodes an AMP deaminase (AMPD), which is also an identified herbicide target. This report identifies an N-terminal transmembrane domain in Arabidopsis FAC1, explores subcellular fractionation, and presents a 3.3-A globular catalytic domain x-ray crystal structure with a bound herbicide-based transition state inhibitor that provides the first glimpse of a complete AMPD active site. FAC1 contains an (alpha/beta)(8)-barrel characterized by loops in place of strands 5 and 6 that places it in a small subset of the amidohydrolase superfamily with imperfect folds. Unlike tetrameric animal orthologs, FAC1 is a dimer and each subunit contains an exposed Walker A motif that may be involved in the dramatic combined K(m) (25-80-fold lower) and V(max) (5-6-fold higher) activation by ATP. Normal mode analysis predicts a hinge motion that flattens basic surfaces on each monomer that flank the dimer interface, which suggests a reversible association between the FAC1 globular catalytic domain and intracellular membranes, with N-terminal transmembrane and disordered linker regions serving as the anchor and attachment to the globular catalytic domain, respectively.

EMBRYONIC FACTOR 1 encodes an AMP deaminase and is essential for the zygote to embryo transition in Arabidopsis.

Fusion of the egg and the sperm cells in plants produces a zygote that develops into an embryo. Screening of ethyl methanesulfonate-mutagenized populations of Arabidopsis led to the identification of EMBRYONIC FACTOR 1 (FAC1), a locus that gives a zygote-lethal phenotype when mutated. The FAC1 gene was identified by positional cloning and confirmed by a genetic complementation test against a T-DNA insertion allele. It encodes an AMP deaminase (AMPD) that is known in human and yeast to convert AMP to IMP to maintain the energy potential. Expression of FAC1 in a yeast AMPD mutant after removal of its N-terminal putative transmembrane domain complemented the mutant phenotype, suggesting a functional conservancy but a structural divergence through evolution. Although a low level of FAC1 expression was observed in all organs tested, using a reporter construct we observed a significantly increased FAC1 expression in the zygote, early embryo and endosperm. Furthermore, during somatic embryogenesis, a high level of FAC1 expression was observed in developing embryos including putative embryogenic cells. FAC1, therefore, represents one of the earliest expressed genes known in plants. It may act through AMP depletion to provide sufficient energy for the zygote to proceed through development.

Frequency of the C34T mutation of the AMPD1 gene in world-class endurance athletes: does this mutation impair performance?

The C34T mutation in the gene encoding for the skeletal muscle-specific isoform of AMP deaminase (AMPD1) is a common mutation among Caucasians (i.e., one of five individuals) that can impair exercise capacity. The purpose of this study was twofold. First, we determined the frequency distribution of the C34T mutation in a group of top-level Caucasian (Spanish) male endurance athletes (cyclists and runners, n = 104). This group was compared with randomly selected Caucasian (Spanish) healthy (asymptomatic) nonathletes (n = 100). The second aim of this study was to compare common laboratory indexes of endurance performance (maximal oxygen uptake or ventilatory thresholds) within the group of athletes depending on their C34T AMPD1 genotype. The frequency of the mutant T allele was lower (P < 0.05) in the group of athletes (4.3%) compared with controls (8.5%). On the other hand, indexes of endurance performance did not differ (P > 0.05) between athlete carriers or noncarriers of the C34T mutation (e.g., maximal oxygen uptake 72.3 +/- 4.6 vs. 73.5 +/- 5.9 ml.kg(-1).min(-1), respectively). In conclusion, although the frequency distribution of the mutant T allele of the AMPD1 genotype is lower in Caucasian elite endurance athletes than in controls, the C34T mutation does not significantly impair endurance performance once the elite-level status has been reached in sports.

Breed differences in the biochemical determinism of ultimate pH in breast muscles of broiler chickens--a key role of AMP deaminase?

The biochemical determinism of ultimate pH (pHu) was studied in the pectoralis muscle of broiler chickens. Thirty birds of 3 genetic types (a fast-growing standard (FG), a slow-growing French "Label Rouge" (SG), and a heavy line type (HL)) were kept under conventional breeding methods until the usual marketing age (6, 12, and 6 wk for FG, SG, and HL birds, respectively). The birds were divided into 3 different antemortem treatment groups: minimum stress, shackling for a longer time (2 min), and heat stress (exposure to 35 degrees C for 3.5 h and shackling for 2 min before stunning). The birds were slaughtered on the same day. The pHu differed (P < 0.001) among the 3 genetic types, ranking as follows: FG (5.95+/-0.01) > HL (5.85+/-0.02) > SG (5.73+/-0.02). In SG and HL birds, pHu was strongly correlated with muscle glycogen content at slaughter (r = -0.74 and -0.82; P < 0.01 respectively), whereas this correlation was weak in FG birds. Regardless of genetic type, neither buffering capacity nor lactate accumulation significantly contributed to pHu variations (P > 0.05). The activity of adenosine monophosphate deaminase (AMPd) was significantly higher in FG chickens (0.98+/-0.31; P < 0.05) than in HL and SG birds (0.46+/-0.24 and 0.34+/-0.18, respectively). Significant correlations were found between AMPd activity, pHu, and glycolytic potential (GP) at slaughter (r = 0.34 and -.29; P < 0.01, respectively). Further research is needed to study in more detail the role of AMPd in the determinism of pHu, particularly in fast-growing broilers.

Ecto-AMP deaminase blunts the ATP-derived adenosine A2A receptor facilitation of acetylcholine release at rat motor nerve endings.

At synapses, ATP is released and metabolised through ecto-nucleotidases forming adenosine, which modulates neurotransmitter release through inhibitory A1 or facilitatory A2A receptors, according to the amounts of extracellular adenosine. Neuromuscular junctions possess an ecto-AMP deaminase that can dissociate extracellular ATP catabolism from adenosine formation. In this study we have investigated the pattern of ATP release and its conversion into adenosine, to probe the role of ecto-AMP deaminase in controlling acetylcholine release from rat phrenic nerve terminals. Nerve-evoked ATP release was 28 +/- 12 pmol (mg tissue)-1 at 1 Hz, 54 +/- 3 pmol (mg tissue)-1 at 5 Hz and disproportionally higher at 50 Hz (324 +/- 23 pmol (mg tissue)-1). Extracellular ATP (30 microM) was metabolised with a half time of 8 +/- 2 min, being converted into ADP then into AMP. AMP was either dephosphorylated into adenosine by ecto-5'-nucleotidase (inhibited by ATP and blocked by 200 microM alpha,beta-methylene ADP) or deaminated into IMP by ecto-AMP deaminase (inhibited by 200 microM deoxycoformycin, which increased adenosine formation). Dephosphorylation and deamination pathways also catabolised endogenously released adenine nucleotides, since the nerve-evoked extracellular AMP accumulation was increased by either alpha,beta-methylene ADP (200 microM) or deoxycoformycin (200 microM). In the presence of nitrobenzylthioinosine (30 microM) to inhibit adenosine transport, deoxycoformycin (200 microM) facilitated nerve-evoked [3H]acetylcholine release by 77 +/- 9 %, an effect prevented by the A2A receptor antagonist, ZM 241385 (10 nM). It is concluded that, while ecto-5'-nucleotidase is inhibited by released ATP, ecto-AMP deaminase activity transiently blunts adenosine formation, which would otherwise reach levels high enough to activate facilitatory A2A receptors on motor nerve terminals.

Influence on myoadenylate deaminase function in rat skeletal muscle after homologous and heterologous immunization with the purified enzyme.

The aim of the study was to shed some light on the possibility of anti-MAD autoantibodies in cases of rhabdomyolysis or microtraumatic muscular damage causing the symptoms of the acquired myoadenylate deaminase deficiency. Therefore a homologous and a heterologous immunization of rats was carried out with myoadenylate deaminase (MAD; EC 3.5.4.6.) isolated from rat white gastrocnemius muscle (type IIb) and rabbit skeletal muscle. Antibody response to homologous and heterologous antigens was quantified by ELISA and by the inhibition of MAD activity in vitro. Anti-MAD IgG antibodies obtained by homologous immunization caused an inhibition rate of 80% when using MAD from rat white gastrocnemius muscle. Furthermore, the function of MAD in homologously and heterologously immunized rats was investigated after maximal swimming exercise in comparison to non-immunized animals by determination of muscle ammonia and by HPLC detection of inosine 5'-monophosphate (IMP) in skeletal muscle tissues. Both IMP and ammonia accumulation were significantly reduced in type IIb muscle fibers after homologous immunization of rats compared to non-immunized controls (n = 7), whereas the concentration of muscle lactate showed no differences. According to these results we propose that by homologous immunization with purified MAD, anti-MAD IgG impairs the function of cytoplasmic MAD during vigorous exercise in vivo.

Isolation and regulatory mechanisms of smooth muscle AMP-deaminase.

AMP-deaminase from cow uterine smooth muscle has been purified. The enzyme activity is regulated by the two cooperating mechanisms: allosteric and dissociation--association.

Functional significance of AMP deaminase and adenosine deaminase in the aestivating freshwater snail, Pila globosa (swainson): possible neuroendocrine involvement.

The functional significance of AMP deaminase and adenosine deaminase has been studied in hepatopancreas of active, aestivated and ganglionic extracts-administered snails. The activity levels of both enzymes decreased in aestivating snails. Active snails injected with ganglionic extracts of aestivated snails also showed decreased activity. Contrastingly, the hepatopancreas of aestivated snails when treated with ganglionic extracts of active snails showed increased specific activities of both enzymes. The decrease or increase in the specific activities varied with different ganglionic extracts and the significance of the same is discussed.

Alterations in nucleotide pools induced by 3-deazaadenosine and related compounds. Role of adenylate deaminase.

3-Deazaadenine, 3-deazaadenosine, and the carbocyclic analog of 3-deazaadenosine produced similar effects on nucleotide pools of L1210 cells in culture: each caused an increase in IMP and a decrease in adenine nucleotides and had no effect on nucleotides of uracil and cytosine. Concentrations of 50-100 microM were required to produce these effects. Although 3-deazaadenosine and carbocyclic 3-deazaadenosine are known to be potent inhibitors of adenosylhomocysteine hydrolase, the effects on nucleotide pools apparently are not mediated via this inhibition because they are also produced by the base, 3-deazaadenine, and because the concentrations required are higher than those required to inhibit the hydrolase. Cells grown in the presence of 3-deazaadenine or 3-deazaadenosine contained phosphates of 3-deazaadenosine (the mono- and triphosphates were isolated); from cells grown in the presence of the carbocyclic analog of 3-deazaadenosine, the monophosphate was isolated, but evidence for the presence of the triphosphate was not obtained. A cell-free supernatant fraction from L1210 cells supplemented with ATP catalyzed the formation of monophosphates from 3-deazaadenosine or carbocyclic 3-deazaadenosine, and a cell-free supernatant fraction supplemented with 5-phosphoribosyl 1-pyrophosphate (PRPP) catalyzed the formation of 3-deaza-AMP from 3-deazaadenine. Adenosine kinase apparently was not solely responsible for the phosphorylation of the nucleosides because a cell line that lacked this enzyme converted 3-deazaadenosine to phosphates. No evidence was obtained that the effects on nucleotide pools resulted from a block of the IMP-AMP conversion, but the results could be rationalized as a consequence of increased AMP deaminase activity. This explanation is supported by two observations: (a) coformycin, an inhibitor of AMP deaminase, prevented the effects on nucleotide pools, and (b) 3-deazaadenine decreased the conversion of carbocyclic adenosine to carbocyclic ATP and increased its conversion to carbocyclic GTP. The latter conversion requires the action of AMP deaminase and the observed effects can be rationalized by a nucleoside analog-mediated increase in AMP deaminase activity. Because these effects on nucleotide pools are produced only by concentrations higher than those required to inhibit adenosylhomocysteine hydrolase, they may not contribute significantly to the biological effects of 3-deazaadenosine or carbocyclic 3-deazaadenosine.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of AMP deaminase reaction in the response of phosphofructokinase to the adenylate energy charge.

The role of NH+4 ion and AMP deaminase reaction in the activation of phosphofructokinase with respect to its response to the adenylate energy charge was investigated using permeabilized yeast cells. (a) Phosphofructokinase and AMP deaminase were activated by the decrease in the adenylate energy charge. The addition of NH+4 further stimulated the phosphofructokinase activity in the presence of intracellular level of K+, and the optimal energy charge value giving the maximal response of the enzyme was shifted from 0.3 to the value above 0.5. (b) The increase in NH+4 ion produced through the activation of AMP deaminase by spermine which shows no direct action on the phosphofructokinase activity can activate phosphofructokinase with shift of the optimal energy charge value of the enzyme to 0.5 in the presence of K+, whereas the optimal energy charge value for AMP deaminase reaction was not affected by the addition of spermine. Phosphofructokinase can be activated most effectively by the physiological decrease in the energy charge under the condition of increased NH+4 in the presence of K+. The possibility that the interaction of phosphofructokinase with AMP deaminase under hypoxic condition might be a contributing factor to the Pasteur effect is discussed.

[AMP-aminohydrolase of the brain and other organs and the regulation of its activity]. / AMF-aminogidrolaza mozga i drugikh organov i reguliatsiia ee aktivnosti.

Present concepts of the hydrolytic deamination of adenylic acid through AMP-aminohydrolase of brain and other tissues are discussed. The content of AMP-aminohydrolase of tissues, its intracellular disposition, physico-chemical properties, physiological role and the regulation of its activity are considered. AMP-aminohydrolase of brain is compared with that of other tissues (muscle, liver, kidney, erythrocytes, etc.), and characteristic features of the regulation of its activity in brain tissue is included. The participation of nucleotides, phosphoorganic compounds, hexokinase and some cations in the regulation of AMP-aminohydrolase activity of brain and other tissues are discussed on the basis of the experiments carried out and the data available.