852 research outputs found
Ketahanan Kadar Vitamin C Dan Kadar Air Pada Cabai Merah Besar (Capsicum Annuuml) Dengan Berbagai Jenis Kemasan
Resistance levels of vitamin cand water content on a large red chillies (capsicum annuuml.) With different types of packaging The aim of this study is to obtain a type of packaging that can preserve high levels of vitamin C and low moisture loss. This research used Completely Randomized Design (CRD), consisting of four packaging treatments which are A. Poliethylen plastic; B. gunny; C. Palm leaf material; D. without packaging. Each treatment was repeated five times with total of twenty trials. There was an effect on water content and the levels of vitamin C. Poliethylen plastic packaging is not significantly different with palm leaf material packaging in loss of low water levels and a high content of vitamin C levels obtained. Low vitamin C and low water content was obtained on treatment with gunny packaging and without packaging
EMS, Suicide, and the Out-of-Hospital DNR Order
Patient autonomy may be placed at odds with the “rescue mentality” of EMS personnel when they are summoned and an out-of-hospital do not resuscitate order (DNR) is in place. This is exacerbated when a valid patient DNR order and a patient suicide attempt exist concurrently. This paper explores the two medical ethics principles of autonomy and beneficence placed at risk and the moral considerations for EMS personnel when a valid out-of-hospital DNR, a patient attempt at suicide, and a call to 911 intersect in the same temporal period
Invariant Aspartic Acid in Muscle Nicotinic Receptor Contributes Selectively to the Kinetics of Agonist Binding
We examined functional contributions of interdomain contacts within the nicotinic receptor ligand binding site using single channel kinetic analyses, site-directed mutagenesis, and a homology model of the major extracellular region. At the principal face of the binding site, the invariant αD89 forms a highly conserved interdomain contact near αT148, αW149, and αT150. Patch-clamp recordings show that the mutation αD89N markedly slows acetylcholine (ACh) binding to receptors in the resting closed state, but does not affect rates of channel opening and closing. Neither αT148L, αT150A, nor mutations at both positions substantially affects the kinetics of receptor activation, showing that hydroxyl side chains at these positions are not hydrogen bond donors for the strong acceptor αD89. However substituting a negative charge at αT148, but not at αT150, counteracts the effect of αD89N, demonstrating that a negative charge in the region of interdomain contact confers rapid association of ACh. Interpreted within the structural framework of ACh binding protein and a homology model of the receptor ligand binding site, these results implicate main chain amide groups in the domain harboring αW149 as principal hydrogen bond donors for αD89. The specific effect of αD89N on ACh association suggests that interdomain hydrogen bonding positions αW149 for optimal interaction with ACh
Initial Coupling of Binding to Gating Mediated by Conserved Residues in the Muscle Nicotinic Receptor
We examined functional consequences of intrasubunit contacts in the nicotinic receptor α subunit using single channel kinetic analysis, site-directed mutagenesis, and structural modeling. At the periphery of the ACh binding site, our structural model shows that side chains of the conserved residues αK145, αD200, and αY190 converge to form putative electrostatic interactions. Structurally conservative mutations of each residue profoundly impair gating of the receptor channel, primarily by slowing the rate of channel opening. The combined mutations αD200N and αK145Q impair channel gating to the same extent as either single mutation, while αK145E counteracts the impaired gating due to αD200K, further suggesting electrostatic interaction between these residues. Interpreted in light of the crystal structure of acetylcholine binding protein (AChBP) with bound carbamylcholine (CCh), the results suggest in the absence of ACh, αK145 and αD200 form a salt bridge associated with the closed state of the channel. When ACh binds, αY190 moves toward the center of the binding cleft to stabilize the agonist, and its aromatic hydroxyl group approaches αK145, which in turn loosens its contact with αD200. The positional changes of αK145 and αD200 are proposed to initiate the cascade of perturbations that opens the receptor channel: the first perturbation is of β-strand 7, which harbors αK145 and is part of the signature Cys-loop, and the second is of β-strand 10, which harbors αD200 and connects to the M1 domain. Thus, interplay between these three conserved residues relays the initial conformational change from the ACh binding site toward the ion channel
Mechanism of Tacrine Block at Adult Human Muscle Nicotinic Acetylcholine Receptors
We used single-channel kinetic analysis to study the inhibitory effects of tacrine on human adult nicotinic receptors (nAChRs) transiently expressed in HEK 293 cells. Single channel recording from cell-attached patches revealed concentration- and voltage-dependent decreases in mean channel open probability produced by tacrine (IC50 4.6 μM at −70 mV, 1.6 μM at −150 mV). Two main effects of tacrine were apparent in the open- and closed-time distributions. First, the mean channel open time decreased with increasing tacrine concentration in a voltage-dependent manner, strongly suggesting that tacrine acts as an open-channel blocker. Second, tacrine produced a new class of closings whose duration increased with increasing tacrine concentration. Concentration dependence of closed-times is not predicted by sequential models of channel block, suggesting that tacrine blocks the nAChR by an unusual mechanism. To probe tacrine's mechanism of action we fitted a series of kinetic models to our data using maximum likelihood techniques. Models incorporating two tacrine binding sites in the open receptor channel gave dramatically improved fits to our data compared with the classic sequential model, which contains one site. Improved fits relative to the sequential model were also obtained with schemes incorporating a binding site in the closed channel, but only if it is assumed that the channel cannot gate with tacrine bound. Overall, the best description of our data was obtained with a model that combined two binding sites in the open channel with a single site in the closed state of the receptor
Potentiation of a neuronal nicotinic receptor via pseudo-agonist site
Neuronal nicotinic receptors containing α4 and β2 subunits assemble in two pentameric stoichiometries, (α4)3(β2)2 and (α4)2(β2)3, each with distinct pharmacological signatures; (α4)3(β2)2 receptors are strongly potentiated by the drug NS9283, whereas (α4)2(β2)3 receptors are unaffected. Despite this stoichiometry-selective pharmacology, the molecular identity of the target for NS9283 remains elusive. Here, studying (α4)3(β2)2 receptors, we show that mutations at either the principal face of the β2 subunit or the complementary face of the α4 subunit prevent NS9283 potentiation of ACh-elicited single-channel currents, suggesting the drug targets the β2–α4 pseudo-agonist sites, the α4–α4 agonist site, or both sites. To distinguish among these possibilities, we generated concatemeric receptors with mutations at specified subunit interfaces, and monitored the ability of NS9283 to potentiate ACh-elicited single-channel currents. We find that a mutation at the principal face of the β2 subunit at either β2–α4 pseudo-agonist site suppresses potentiation, whereas mutation at the complementary face of the α4 subunit at the α4–α4 agonist site allows a significant potentiation. Thus, monitoring potentiation of single concatemeric receptor channels reveals that the β2–α4 pseudo-agonist sites are required for stoichiometry-selective drug action. Together with the recently determined structure of the (α4)3(β2)2 receptor, the findings have implications for structure-guided drug design
Nicotinic Receptor Interloop Proline Anchors β1-β2 and Cys loops in Coupling Agonist Binding to Channel Gating
Nicotinic acetylcholine receptors (AChRs) mediate rapid excitatory synaptic transmission throughout the peripheral and central nervous systems. They transduce binding of nerve-released ACh into opening of an intrinsic channel, yet the structural basis underlying transduction is not fully understood. Previous studies revealed a principal transduction pathway in which αArg 209 of the pre-M1 domain and αGlu 45 of the β1–β2 loop functionally link the two regions, positioning αVal 46 of the β1–β2 loop in a cavity formed by αPro 272 through αSer 269 of the M2–M3 loop. Here we investigate contributions of residues within and proximal to this pathway using single-channel kinetic analysis, site-directed mutagenesis, and thermodynamic mutant cycle analysis. We find that in contributing to channel gating, αVal 46 and αVal 132 of the signature Cys loop couple energetically to αPro 272. Furthermore, these residues are optimized in both their size and hydrophobicity to mediate rapid and efficient channel gating, suggesting naturally occurring substitutions at these positions enable a diverse range of gating rate constants among the Cys-loop receptor superfamily. The overall results indicate that αPro 272 functionally couples to flanking Val residues extending from the β1–β2 and Cys loops within the ACh binding to channel opening transduction pathway
QSAR development and profiling of 72,524 REACH substances for PXR activation and CYP3A4 induction
- …