Mutations in a conserved residue in the influenza virus neuraminidase active site decreases sensitivity to Neu5Ac2en-derived inhibitors

The influenza virus neuraminidase (NA)-specific inhibitor zanamivir (4-guanidino-Neu5Ac2en) is effective in humans when administered topically within the respiratory tract. The search for compounds with altered pharmacological properties has led to the identification of a novel series of influenza virus NA inhibitors in which the triol group of zanamivir has been replaced by a hydrophobic group linked by a carboxamide at the 6 position (6-carboxamide). NWS/G70C variants generated in vitro, with decreased sensitivity to 6-carboxamide, contained hemagglutinin (HA) and/or NA mutations. HA mutants bound with a decreased efficiency to the cellular receptor and were cross-resistant to all the NA inhibitors tested. The NA mutation, an Arg-to-Lys mutation, was in a previously conserved site, Arg292, which forms part of a triarginyl cluster in the catalytic site. In enzyme assays, the NA was equally resistant to zanamivir and 4-amino-Neu5Ac2en but showed greater resistance to 6-carboxamide and was most resistant to a new carbocyclic NA inhibitor, GS4071, which also has a hydrophobic side chain at the 6 position. Consistent with enzyme assays, the lowest resistance in cell culture was seen to zanamivir, more resistance was seen to 6-carboxamide, and the greatest resistance was seen to GS4071. Substrate binding and enzyme activity were also decreased in the mutant, and consequently, virus replication in both plaque assays and liquid culture was compromised. Altered binding of the hydrophobic side chain at the 6 position or the triol group could account for the decreased binding of both the NA inhibitors and substrate.     

Mutation in the influenza virus neuraminidase gene resulting in decreased sensitivity to the neuraminidase inhibitor 4-guanidino-Neu5Ac2en leads to instability of the enzyme

We previously isolated a variant of the influenza virus NWS/G70C, with a decreased sensitivity to the neuraminidase-specific inhibitor 4-guanidino-Neu5Ac2en in vitro, which has a mutation in one of the conserved residues of the neuraminidase Glu 119 to Gly. Despite the mutation, purified neuraminidase demonstrated the same specific activity as the parent neuraminidase. In contrast, characterization of a similar mutant by another group revealed a low specific activity of the enzyme. We confirm here that the specific activity of our variant is the same as that of the parent, but report that this mutation makes the enzyme inherently unstable, at high and low temperatures, either on the virion or as purified neuraminidase. Thus, for a valid determination of specific activity the concentration of native NA needs to be determined at the time of enzyme assay. Structurally, the instability may be partially explained by the introduction of a side chain (Gly), which carries a greater entropy penalty in condensation of the structure from the unfolded to the folded state and this, together with the loss of stabilizing interaction between Glu 119 and its neighbors in the active site, is not compensated for by the water molecule occupying the position of the carboxylate group (6).     

ADP-induced platelet activation

Platelet activation is central to the pathogenesis of hemostasis and arterial thrombosis. Platelet aggregation plays a major role in acute coronary artery diseases, myocardial infarction, unstable angina, and stroke. ADP is the first known and an important agonist for platelet aggregation. ADP not only causes primary aggregation of platelets but is also responsible for the secondary aggregation induced by ADP and other agonists. ADP also induces platelet shape change, secretion from storage granules, influx and intracellular mobilization of Ca2+, and inhibition of stimulated adenylyl cyclase activity. The ADP-receptor protein mediating ADP-induced platelet responses has neither been purified nor cloned. Therefore, signal transduction mechanisms underlying ADP-induced platelet responses either remain uncertain or less well understood. Recent contributions from chemists, biochemists, cell biologists, pharmacologists, molecular biologists, and clinical investigators have added considerably to and enhanced our knowledge of ADP-induced platelet responses. Although considerable efforts have been directed toward identifying and cloning the ADP-receptor, these have not been completely successful or without controversy. Considerable progress has been made toward understanding the mechanisms of ADP-induced platelet responses but disagreements persist. New drugs that do not mimic ADP have been found to inhibit fairly selectively ADP-induced platelet activation ex vivo. Drugs that mimic ADP and selectively act at the platelet ADP-receptor have been designed, synthesized, and evaluated for their therapeutic efficacy to block selectively ADP-induced platelet responses. This review examines in detail the developments that have taken place to identify the ADP-receptor protein and to better understand mechanisms underlying ADP-induced platelet responses to develop strategies for designing innovative drugs that block ADP-induced platelet responses by acting selectively at the ADP-receptor and/or by selectively interfering with components of ADP-induced platelet activation mechanisms.     

Cyclic AMP phosphodiesterases in human lymphocytes

The function of lymphocytes, like platelets, has been shown to be inhibited by agents which increase intracellular cyclic AMP. Two high-affinity cAMP phosphodiesterases (PDEs), the cyclic GMP-inhibited cAMP phosphodiesterase, PDE3, and the cAMP-specific phosphodiesterase PDE4, are known to regulate cAMP concentration in haemopoietic cells by degrading cAMP to AMP. We characterized the relative contribution of the two PDEs to total lymphocyte PDE activity. We then determined which of the different gene products, PDE3A, typical of myocardium and platelets, or PDE3B, typical of adipocytes, were present in lymphocytes. The PDE3-specific inhibitor, milrinone, and the PDE4 inhibitor, rolipram, suppressed hydrolysis by 70% and 30% respectively, which indicated that both PDE4 and PDE3 were present, and that PDE3 was predominant. RT-PCR yields the expected size fragment for the primer pair PDE3B and not for PDE3A. The DNA sequence obtained had >95% identity with PDE3B. PDE3B appears to be the major cAMP PDE in lymphocytes. In contrast to human platelets, human lymphocytes appear to contain the PDE3B subtype. Since PDE3B in adipocytes is subject to hormonal regulation, lymphocytes may be similarly modulated. Understanding the role of cAMP regulation and the involvement of cAMP in lymphocyte function may have important implications in drug development.     

THE ARCHITECTURAL NARRATIVE: On Michael Speaks' Ruminations on a ‘Big,Soft, Orange’

The Big, Soft, Orange exhibition on four Dutch architectural firms focuses on the (soft) processes these architects have evolved for dealing with the large scope(big) of contemporary architectural undertakings and the particular historical and geographical conditions these attempts address in the contemporary Netherlands (orange). Following the precedent of the curator. Michael Speaks' comments, the content of the exhibition will be seen to have broader relevance for Architecture. Speaks' own circumstance is considerably influenced by his relationship with, and critique of the work of, Frederic Jameson. By reading between Jameson and Speaks, this paper will use Speaks' exhibition to question the success of the architecture of postmodernity's preoccupation with overtuming the modern-modernism's Utopian assertions, its preoccupation with form, its totalising tendency, and the strictures of the ‘handed-down’ discipline of architecture with a telos in Building.From a Heideggerian perspective the paper will consider the architectural process as the concrete materialisation of the narrative of architectural production informs other than, but leading toward, the traditionally privileged architectural form: Building. Rather than the architectural approaches of postmodernity overturning modernism,it will be concluded that these approaches are merely innovative differentiation as they ‘flesh-out’ and articulate hitherto unformed narratives already extant within the reductive frames of modernity     

集成混频和放大功能的低价电路

在很多应用中,频率变换级包括有一只缓冲器,最好还有一些额外的电压增益电路;一只混频器:还有一些滤波电路.可以简单地将混频器功能与放大器集成起来,从而省掉混频器前的放大器.     

Hyperinsulinemia is not a cause of cortisol-induced hypertension

There is much interest in the relationship of hypertension to hyperinsulinemia. Six male volunteers received cortisol, 50 mg orally four times daily, for 5 days. Plasma insulin concentration increased from 11.8 +/- 3.0 mU/L to 16.1 +/- 4.0 mU/L (P = .034). Fasting glucose increased from 4.7 +/- 0.3 to 5.8 +/- 0.1 mmol/L (P = .001). The insulin-to-glucose ratio was unchanged. Octreotide has been reported to lower blood pressure in obese, hyperinsulinemic, hypertensive patients. The hypothesis that cortisol-induced hypertension might be secondary to steroid-induced hyperinsulinemia was examined by determining whether reversal of hyperinsulinemia by octreotide would reverse cortisol-induced hypertension. Five healthy men were given two subcutaneous injections of 0.05 mg of octreotide before and on the fifth day of cortisol administration. Cortisol increased blood pressure, weight, plasma glucose concentration, and white cell count, with decreases in plasma potassium concentration and packed cell volume. Plasma cortisol concentrations were unchanged following octreotide in the control period but decreased after cortisol treatment. Insulin concentrations were reduced profoundly after octreotide, both in the control period (12.5 +/- 3.7 mU/L, falling to 1.1 +/- 0.3 mU/L at 30 min) and on cortisol (22.3 +/- 4.5 to 2.3 +/- 0.5 mU/L at 30 min). Octreotide did not lower pressure before or after cortisol treatment. Thus, octreotide was effective in lowering plasma insulin concentrations but di not lower blood pressure in normal subjects with cortisol-induced hypertension. These data do not support the notion that steroid-induced hyperinsulinemia is responsible for steroid-induced hypertension.     

An oxygen-consuming phantom simulating perfused tissue to explore oxygen dynamics and <Superscript>19</Superscript>F MRI oximetry

Objective  

This study presents a reproducible phantom which mimics oxygen-consuming tissue and can be used for the validation of ¹⁹F MRI oximetry.