Showing papers on "Polyamine binding published in 1996"
TL;DR: There is no clear knowledge regarding an understanding of the reported effects of selegiline on the progression of Parkinson's disease, but some evidence suggests both an indirect (via induction of radical-scavenging enzymes) and a direct antioxidant function for seLegiline.
Abstract: The acetylenic selective monoamine oxidase (MAO) type B suicide inhibitor selegiline (previously called L-deprenyl) has proved to be a useful adjuvant to levodopa therapy and monotherapy of Parkinson's disease (PD). Selegiline is readily absorbed from the gastrointestinal tract and rapidly enters the brain and spinal cord following oral administration. The drug binds to brain regions with a high MAO-B content, such as the thalamus, the striatum, the cortex, and the brainstem. It is extensively metabolized in humans, mainly in the liver, to form desmethylselegiline and methamphetamine, which are further metabolized to amphetamine. Eighty-six percent of the 10-mg dose was recovered in the urine within 24 hours. These data suggest that accumulation of metabolites does not occur. Although not all features of its anti-PD action are known, studies using brain obtained at autopsy from patients who had been treated with 10 mg of selegiline showed that selective inhibition of MAO-B, with the concomitant increase of phenylethylamine and dopamine (DA) but not of serotonin or noradrenaline, in the basal ganglia may be regarded as its mode of action. The protective effects afforded by selegiline in PD, resulting in a delayed need for levodopa therapy, have been variously interpreted in terms of the involvement of an endogenous neurotoxin or an oxygen free radical mechanism (oxidative stress) in the development of PD. However, although many different hypotheses have been advanced and recent findings have emphasized the significance of oxidative stress in the pathogenesis of the disease, the cause of chronic nigral cell death and the underlying mechanisms remain, as yet, elusive. Therefore, there is no clear knowledge regarding an understanding of the reported effects of selegiline on the progression of PD. Nevertheless, selegiline might be expected to have some protective effects in reducing the production of potentially neurotoxic compounds resulting in the MAO-catalyzed oxidation of DA. In addition, some evidence suggests both an indirect (via induction of radical-scavenging enzymes) and a direct antioxidant function for selegiline. On the other hand, the reported protective effect of selegiline might also receive a contribution from the diminished potentiation of the N-methyl-D-aspartate receptor by the polyamine binding site. Finally, the effects of selegiline might also involve preventing, or perhaps to some extent reversing, the decline in resistance normally associated with cellular aging because of its neurotrophine-like action. However, even in the early clinical stage of PD, the sequence of events leading to nigral cell death may be too far advanced for selegiline to exhibit its maximum potential.
146 citations
TL;DR: The results reveal the potential use of porins as targets for blocking agents and suggest that polyamines may act as endogenous modulators of outer membrane permeability.
Abstract: The permeability of the outer membranes of gram-negative bacteria to hydrophilic compounds is mostly due to the presence of porin channels We tested the effects of four polyamines (putrescine, cadaverine, spermidine, and spermine) on two processes known to depend on intact porin function: fluxes of beta-lactam antibiotics in live cells and chemotaxis In both cases, inhibition was observed Measurements of the rate of permeation of cephaloridine and of chemotaxis in swarm plates and capillary assays were used to determine the concentration dependence of this modulation The effective concentration ranges depended on the nature of the polyamine and varied from submillimolar for spermine to tens of millimolar for cadaverine Both OmpC and OmpF porins were inhibited, although the effects on OmpC appeared to be milder These results are in agreement with our observations that polyamines inhibit porin-mediated ion fluxes in electrophysiological experiments, and they suggest that a low-affinity polyamine binding site might exist in these porins These results reveal the potential use of porins as targets for blocking agents and suggest that polyamines may act as endogenous modulators of outer membrane permeability
110 citations
TL;DR: The comparison of the PotD structure with the two maltodextrin-binding protein structures, determined in the presence and absence of the substrate, suggests that spermidine binding rearranges the relative orientation of thePotD domains to create a more compact structure.
87 citations
Journal Article•
TL;DR: To study the role of acidic residues in modulation of NMDA receptors by spermine, site-directed mutagenesis of receptor subunits and voltage-clamp recording in Xenopus oocytes was used and mutated glutamate and aspartate residues located in the first two thirds of the putative extracellular loop of the NR1A subunit were individually mutated.
Abstract: To study the role of acidic residues in modulation of NMDA receptors by spermine, we used site-directed mutagenesis of receptor subunits and voltage-clamp recording in Xenopus oocytes. Sixteen glutamate and aspartate residues, located in the first two thirds of the putative extracellular loop of the NR1A subunit, were individually mutated. This region of NR1A shows homology with bacterial amino acid binding proteins, a bacterial polyamine binding protein, and a bacterial spermidine acetyltransferase. Mutation of D669 to asparagine (D669N), alanine (D669A), or glutamate (D669E) abolished the "glycine-independent" form of spermine stimulation in heteromeric NR1A/NR2B receptors. These mutations also markedly reduced inhibition by ifenprodil and by protons at NR1A/NR2B receptors. Mutations at the equivalent position (D690) in NR1B, which contains the insert encoded by exon 5, reduced the pH sensitivity of NR1B/NR2B receptors. Thus, the effects of mutations at D669 are not prevented by the presence of exon 5, and the influence of exon 5 is not prevented by mutations at D669 (D690 in NR1B). Mutations at NR1A (D669) had little or no effect on the potencies of glutamate and glycine and did not alter voltage-dependent block by Mg2+ or the "glycine-dependent" form of spermine stimulation. Surprisingly, the D669N and D669A mutations, but not the D669E mutation, reduced voltage-dependent block by spermine at NR1A/NR2 receptors. Mutations in NR2B at a position (D668) equivalent to D669 did not alter spermine stimulation or sensitivity to pH and ifenprodil. However, mutations D668N and D668A but not D668E in NR2B reduced voltage-dependent block by spermine. Screening of the negative charges at NR1A(D669) and NR2B(D668) may be involved in voltage-dependent block by spermine. D669 in NR1A could form part of a binding site for polyamines and ifenprodil and/or part of the proton sensor of the NMDA receptor. Alternatively, this residue may be critical for coupling of modulators such as spermine, protons, and ifenprodil to channel gating.
87 citations
TL;DR: Spermidine-binding sites on PotD protein, a substrate-binding protein in periplasm, in the spermidin-preferential uptake system in Escherichia coli were studied by measuring polyamine transport activities of right-side-out membrane vesicles with mutated PotD proteins prepared by site-directed mutagenesis of the potD gene.
83 citations
TL;DR: The crystal structure of the E. coli PotD protein complexed with spermidine was solved at 1.8 Å resolution and revealed the detailed substrate‐binding mechanism and provided the detailed conformation of the bound sperMidine.
Abstract: The PotD protein from Escherichia coli is one of the components of the polyamine transport system present in the periplasm. This component specifically binds either spermidine or putrescine. The crystal structure of the E. coli PotD protein complexed with spermidine was solved at 1.8 A resolution and revealed the detailed substrate-binding mechanism. The structure provided the detailed conformation of the bound spermidine. Furthermore, a water molecule was clearly identified in the binding site lying between the amino-terminal domain and carboxyl-terminal domain. Through this water molecule, the bound spermidine molecule forms two hydrogen bonds with Thr 35 and Ser 211. Another periplasmic component of polyamine transport, the PotF protein, exhibits 35% sequence identity with the PotD protein, and it binds only putrescine, not spermidine. To understand these different substrate specificities, model building of the PotF protein was performed on the basis of the PotD crystal structure. The hypothetical structure suggests that the side chain of Lys 349 in PotF inhibits spermidine binding because of the repulsive forces between its positive charge and spermidine. On the other hand, putrescine could be accommodated into the binding site without any steric hindrance because its molecular size is much smaller than that of spermidine, and the positively charged amino group is relatively distant from Lys 349.
58 citations
TL;DR: The results presented here suggest that specific spermidine binding occurs mainly with the protein component of the plasma membrane, and was markedly reduced by the presence of divalent cations, such as Mg2+ and Ca2+, whereas it was stimulated by monovalent cations.
Abstract: The general features of [14C]spermidine binding to plasmalemma vesicles isolated from zucchini (Cucurbita pepo L.) etiolated hypocotyls are reported in the present paper. The specific interaction of the polyamine with the plasma membranes was reversible and thermolabile, since it decreased by about 50% in the assay performed at 40[deg]C compared to that carried out on ice. On the contrary, nonspecific binding was unaffected by temperature. Specific spermidine binding showed a pH dependence with a maximum at pH 8.0 and it reached saturation between 0.75 and 1 mM external spermidine concentration. The value of the dissociation constant calculated from Scatchard analysis was 4.4 x 10–5 M. Specific spermidine interaction appeared to be sensitive to detergents and was markedly reduced by the presence of divalent cations, such as Mg2+ and Ca2+, whereas it was stimulated by monovalent cations. Polyamine binding sites were highly sensitive to pronase treatment. Competition experiments, performed using a series of compounds structurally related to spermidine, may provide some indication of the characteristics of spermidine binding sites. The results presented here suggest that specific spermidine binding occurs mainly with the protein component of the plasma membrane.
53 citations
TL;DR: It is proposed that in addition to a slow gating mechanism producing long lasting open and closed states, there is a distinct, intrinsic fast gating process amplified by cytoplasmic Mg2+ and/or polyamine binding to the channel.
40 citations
TL;DR: The concept that excitotoxicity is linked with the generation of free radicals is considered and how selegiline might exert its neuroprotective effects via indirect actions on the polyamine binding site of the NMDA receptor is discussed.
Abstract: There have been many claims that the selective monoamine oxidase type B (MAO-B) inhibitor selegiline may have distinct properties in slowing the progression of Parkinson's disease (PD). Degeneration of nigro-striatal dopaminergic neurons is the primary histopathological feature of PD. Although many different hypotheses have been advanced, the cause of chronic nigral cell death and the underlying mechanisms remain elusive as yet. Therefore, there is no clear knowledge regarding an understanding of the reported effects of selegiline on the progression of PD. However, there is a considerable body of indirect evidence that oxidative stress may play a role in the pathogenesis of this illness. Oxidative stress refers to cytotoxic consequences of hydrogen peroxide and oxygen-derived free radicals such as the hydroxyl radical (.OH), the superoxide anion (.O2), and nitric oxide (NO), which are generated as byproducts of normal and aberrant metabolic processes that utilize molecular oxygen. On the other hand, an increasing body of experimental data has implicated excitotoxicity as a mechanism of cell death in both acute and chronic neurological disease. One of the receptor which is particularly involved in the toxic effects of excitatory amino acids is the NMDA (N-methyl-D-aspartate) receptor. Excessive stimulation of this type of receptor by glutamic acid or NMDA agonists leads to a massive influx of calcium ions into the neuron followed by activation of a variety of calcium-dependent enzymes, impaired mitochondrial function, and the generation of free radicals. This article will consider the concept that excitotoxicity is linked with the generation of free radicals. In view of this idea it will be further discussed how selegiline might exert its neuroprotective effects via indirect actions on the polyamine binding site of the NMDA receptor. Under treatment with the MAO-B inhibitor selegiline, the degradation of putrescine via MAO, a key factor in regulating the polyamine metabolism, might be diminished in the Parkinsonian brain, which in turn would suppress the polyamine synthesis. Hence, the reported neuroprotective effect of selegiline might also receive a contribution from the diminished potentiation of the NMDA receptor by the polyamine binding site. On the other hand, since N1-acetylated spermine and spermidine are also good substrates of MAO-B, it is likely that these compounds will be present in the brain in increased concentrations. It therefore seems possible that they will exert a neuroprotective effect via an antagonistic modulation of the polyamine binding site of the NMDA receptor.
22 citations
TL;DR: It is interesting that hirudonine, which is a naturally occurring compound, was thought to act as an agonist at polyamine binding site of the N-methyl-d-aspartate type of glutamate receptor complex, and guanethidine, an antihypertensive agent, inhibit nNOS activity.
Abstract: Since nitric oxide (NO) is synthesized by nitric oxide synthase (NOS) froml-arginine (Arg) which has an amidino group in its molecule, we, examined the effect of 29 kinds of Arg analogues on neuronal NOS (nNOS) activity in the rat brain None of the Arg analogues acted as a substrate for nNOS Diamidinocystamine, hirudonine, and guanethidine inhibited nNOS activity to 673%, 642% and 741%, respectively, but their inhibitory efficiency was lower than NG-monomethyl-l-arginine (to 365%) which is a well known NOS inhibitor Dimethylguanidine and N-benzoylguanidine also significantly inhibited nNOS activity to 880% and 907%, respectively Whereas almost all of the NOS inhibitors previously reported were synthesizdd by substituting the amidino nitrogen of Arg, none of these new inhibitors were substituted at this position Furthermore, hirudonine, which is a naturally occurring compound, was thought to act as an agonist at polyamine binding site of the N-methyl-d-aspartate type of glutamate receptor complex It is also interesting that guanethidine, an antihypertensive agent, inhibit nNOS activity These new drugs are useful for the investigation not only of the chemical nature of nNOS but also of the physiologic function of NO
4 citations