High level of aspartic acid-bond isomerization during the synthesis of an N-linked tau glycopeptide

An increased degree of utilization of the potential N-glycosylation site In the fourth repeat unit of the human tau protein may be involved in the inability of tau to bind to the corresponding tubulin sequence(s) and in the subsequent development of the paired helical filaments of Alzheimer's disease. To model these processes, we synthesized the octadecapeptide spanning this region without sugar, and with the addition of an N-acetyl-glucosamine moiety. The carbohydrate-protected, glycosylated asparagine was incorporated as a building block during conventional Fmoc-solid phase peptide synthesis. While the crude non-glycosylated analog was obtained as a single peptide, two peptides with, the identical, expected masses, in approximately equal amounts, were detected after the cleavage of the peracetylated glycopeptide. Surprisingly, the two glycopeptides switched positions on the reversed-phase high performance liquid chromatogram after removal of the sugar-protecting acetyl groups. Nuclear magnetic resonance spectroscopy and peptide sequencing identified the more hydrophobic deprotected peak as the target peptide, and the more hydrophilic deprotected peak as a peptide analog in which the aspartic acid-bond just preceding the glycosylated asparagine residue was isomerized resulting in the formation of a beta-peptide. The anomalous chromatographic behavior of the acetylated beta-isomer could be explained on the basis of the generation of an extended hydrophobic surface which is not present in any of the other three glycopeptide variants. Repetition of the syntheses, with altered conditions and reagents, revealed reproducibly high levels of aspartic acid-bond isomerization of the glycopeptide as well as lack of isomerization for the non-glycosylated parent analog. If similar increased aspartic acid-bond isomerization occurs in vivo, a protein modification well known to take place for both the amyloid deposits and the neurofibrillary tangles in Alzheimer's disease, this process may explain the aggregation of glycosylated tau into the paired helical filaments in the affected brains. Copyright (C) 1999 European Peptide Society and John Wiley & Sons, Ltd.

The influence of supra-optimal root-zone temperatures on growth and stomatal conductance in Capsicum annuum L.

Pepper (Capsicum annuum L.) plants were grown aeroponically in a Singapore greenhouse under natural diurnally fluctuating ambient shoot temperatures, but at two different root-zone temperatures (RZTs): a constant 20 +/- 2 degrees C RZT and a diurnally fluctuating ambient (A) (25-40 degrees C) RZT, Plants grown at 20-RZT had more leaves, greater leaf area and dry weight than A-RZT plants. Reciprocal transfer experiments were conducted between RZTs to investigate the effect on plant growth, stomatal conductance (g(s)) and water relations. Transfer of plants from A-RZT to 20-RZT increased plant dry weight, leaf area, number of leaves, shoot water potential (Psi(shoot)), and g(s); while transfer of plants from 20-RZT to A-RZT decreased these parameters. Root hydraulic conductivity was measured in the latter transfer and decreased by 80% after 23 d at A-RZT. Transfer of plants from 20-RZT to A-RZT had no effect on xylem ABA concentration or xylem nitrate concentration, but reduced xylem sap pH by 0.2 units. At both RZTs, g(s) measured in the youngest fully expanded leaves increased with plant development. In plants with the same number of leaves, A-RZT plants had a higher g(s) than 20-RZT plants, but only under high atmospheric vapour pressure deficit. The roles of chemical signals and hydraulic factors in controlling g(s) of aeroponically grown Capsicum plants at different RZTs are discussed.

Response of a two-level atom to a narrow-bandwidth squeezed-vacuum excitation

Using the coupled-system approach we calculate the optical spectra of the fluorescence and transmitted fields of a two-level atom driven by a squeezed vacuum of bandwidths smaller than the natural atomic linewidth. We find that in this regime of squeezing bandwidths the spectra exhibit unique features, such as a hole burning and a three-peak structure, which do not appear for a broadband excitation. We show that the features are unique to the quantum nature of the driving squeezed vacuum field and donor appear when the atom is driven by a classically squeezed field. We find that a quantum squeezed-vacuum field produces squeezing in the emitted fluorescence field which appears only in the squeezing spectrum while there is no squeezing in the total field. We also discuss a nonresonant excitation and find that depending on the squeezing bandwidth there is a peak or a hole in the spectrum at a frequency corresponding to a three-wave-mixing process. The hole appears only for a broadband excitation and results from the strong correlations between squeezed-vacuum photons.

Level-one highest weight representations of U-q[g1(1 vertical bar 1)] and associated vertex operators

We study the level-one irreducible highest weight representations of U-q[gl(1\1)] and associated q-vertex operators. We obtain the exchange relations satisfied by these vertex operators. The characters and supercharacters associated with these irreducible representations are calculated'. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Optimal release strategies for biological control agents: an application of stochastic dynamic programming to population management

1. Establishing biological control agents in the field is a major step in any classical biocontrol programme, yet there are few general guidelines to help the practitioner decide what factors might enhance the establishment of such agents. 2. A stochastic dynamic programming (SDP) approach, linked to a metapopulation model, was used to find optimal release strategies (number and size of releases), given constraints on time and the number of biocontrol agents available. By modelling within a decision-making framework we derived rules of thumb that will enable biocontrol workers to choose between management options, depending on the current state of the system. 3. When there are few well-established sites, making a few large releases is the optimal strategy. For other states of the system, the optimal strategy ranges from a few large releases, through a mixed strategy (a variety of release sizes), to many small releases, as the probability of establishment of smaller inocula increases. 4. Given that the probability of establishment is rarely a known entity, we also strongly recommend a mixed strategy in the early stages of a release programme, to accelerate learning and improve the chances of finding the optimal approach.

U-q[(sl(2)over-cap vertical bar 1)] vertex operators, screen currents, and correlation functions at an arbitrary level

Bosonized q-vertex operators related to the four-dimensional evaluation modules of the quantum affine superalgebra U-q[sl((2) over cap\1)] are constructed for arbitrary level k=alpha, where alpha not equal 0,-1 is a complex parameter appearing in the four-dimensional evaluation representations. They are intertwiners among the level-alpha highest weight Fock-Wakimoto modules. Screen currents which commute with the action of U-q[sl((2) over cap/1)] up to total differences are presented. Integral formulas for N-point functions of type I and type II q-vertex operators are proposed. (C) 2000 American Institute of Physics. [S0022-2488(00)00608-3].

Level-one highest weight representation of U-q[sl((N)over-cap vertical bar 1)] and Bosonization of the multicomponent Super t-J model

We study the level-one irreducible highest weight representations of the quantum affine superalgebra U-q[sl((N) over cap\1)], and calculate their characters and supercharacters. We obtain bosonized q-vertex operators acting on the irreducible U-q[sl((N) over cap\1)] modules and derive the exchange relations satisfied by the vertex operators. We give the bosonization of the multicomponent super t-J model by using the bosonized vertex operators. (C) 2000 American Institute of Physics. [S0022- 2488(00)00508-9].

Returns to farm-level soil conservation on tropical steep slopes: The case of the Eritrean highlands

This study conducts an economic analysis of investment in simple soil conservation technologies in the highlands of Eritrea. The data used in the analysis were obtained from a farm survey and supplemented with data from secondary sources. Risk analysis techniques are used to take account of the uncertainties regarding the relationship between soil erosion and crop yield. The financial analysis reveals negative net present values (NPVs) and internal rates of return (IRRs) below 12 per cent for various slope categories. On the other hand, the economic analysis returns positive NPVs and IRRs of over 20 per cent. The results clearly indicate that in-vestment in soil conservation technology may not be a viable short-term proposition from the farmer's point of view and yet the net social benefits are positive. There is a strong case for government to provide incentives for soil conservation in view of the economic benefits.

Saturation of a two-level atom in polychromatic fields

The response of a two-level atom in a strong polychromatic field composed of a large number of equidistant frequency components is investigated. We calculate numerically, as well as analytically,:the stationary population inversion and show that the saturation of the atomic transition strongly depends on whether or not there is a central (resonant) frequency component in the driving field. We find that, in the presence of the central component, the atom can remain in the ground state even for a strong Rabi frequency of the driving field. In addition, we find that the inversion is sensitive to the relative phase between the frequency components. When the central component is suppressed, the atomic transition saturates with the Rabi frequency independent of the relative phase.

Using stochastic dynamic programming to determine optimal fire management for Banksia ornata

1. A model of the population dynamics of Banksia ornata was developed, using stochastic dynamic programming (a state-dependent decision-making tool), to determine optimal fire management strategies that incorporate trade-offs between biodiversity conservation and fuel reduction. 2. The modelled population of B. ornata was described by its age and density, and was exposed to the risk of unplanned fires and stochastic variation in germination success. 3. For a given population in each year, three management strategies were considered: (i) lighting a prescribed fire; (ii) controlling the incidence of unplanned fire; (iii) doing nothing. 4. The optimal management strategy depended on the state of the B. ornata population, with the time since the last fire (age of the population) being the most important variable. Lighting a prescribed fire at an age of less than 30 years was only optimal when the density of seedlings after a fire was low (< 100 plants ha(-1)) or when there were benefits of maintaining a low fuel load by using more frequent fire. 5. Because the cost of management was assumed to be negligible (relative to the value of the persistence of the population), the do-nothing option was never the optimal strategy, although lighting prescribed fires had only marginal benefits when the mean interval between unplanned fires was less than 20-30 years.

Modelling socially optimal land allocations for sugar cane growing in North Queensland: a linked mathematical programming and choice modelling study

A modelling framework is developed to determine the joint economic and environmental net benefits of alternative land allocation strategies. Estimates of community preferences for preservation of natural land, derived from a choice modelling study, are used as input to a model of agricultural production in an optimisation framework. The trade-offs between agricultural production and environmental protection are analysed using the sugar industry of the Herbert River district of north Queensland as an example. Spatially-differentiated resource attributes and the opportunity costs of natural land determine the optimal tradeoffs between production and conservation for a range of sugar prices.

The preparation and execution of self-initiated and externally-triggered movement: A study of event-related fMRI

Studies of functional brain imaging in humans and single cell recordings in monkeys have generally shown preferential involvement of the medially located supplementary motor area (SMA) in self-initiated movement and the lateral premotor cortex in externally cued movement. Studies of event-related cortical potentials recorded during movement preparation, however, generally show increased cortical activity prior to self-initiated movements but little activity at early stages prior to movements that are externally cued at unpredictable times. In this study, the spatial location and relative timing of activation for self-initiated and externally triggered movements were examined using rapid event-related functional MRI. Twelve healthy right-handed subjects were imaged while performing a brief finger sequence movement (three rapid alternating button presses: index-middle-index finger) made either in response to an unpredictably timed auditory cue (between 8 to 24 s after the previous movement) or at self-paced irregular intervals. Both movement conditions involved similar strong activation of medial motor areas including the pre-SMA, SMA proper, and rostral cingulate cortex, as well as activation within contralateral primary motor, superior parietal, and insula cortex. Activation within the basal ganglia was found for self-initiated movements only, while externally triggered movements involved additional bilateral activation of primary auditory cortex. Although the level of SMA and cingulate cortex activation did not differ significantly between movement conditions, the timing of the hemodynamic response within the pre-SMA was significantly earlier for self-initiated compared with externally triggered movements. This clearly reflects involvement of the pre-SMA in early processes associated with the preparation for voluntary movement. (C) 2002 Elsevier Science.

Experiences with redo aortic valve surgery

Objectives and Methods: Reoperations are an integral part of a cardiac surgeon's practice. We share our experience of 546 reoperations over the last 21 years to January 2000, with the focus directed towards the timing of reoperation, reducing the mortality and morbidity of reoperation and rereplacement aortic valve surgery, and understanding the important risk factors. In addition, the precise technical steps that facilitate careful successful explantation of various devices (allograft, stented and stentless xenografts, and mechanical valves) are detailed. Results: Optimal planned reoperation before deterioration to New York Heart Association Class III/IV levels and before unfavorable cardiac and comorbidity general system failure occurs has produced low mortality and morbidity as compared with first operation results. However, unfavorable delays and late rereferral result in mortality rates of up to 22% for emergency redo AVR for degenerated bioprostheses. Conclusion: Cardiac surgical units have the opportunity to establish a closer patient-surgeon relationship, which favors, when necessary, the optimal timing of reoperation. Knowledge of the more important risk factors and adherence to specific technical steps at explantation of various devices enhances satisfactory reoperation outcomes.

Is there a role for axillary dissection for patients with operable breast cancer in this era of conservatism?

Background: The trend in breast cancer surgery is toward more conservative operative procedures. The new staging technique of sentinel node biopsy facilitates the identification of pathological node-negative patients in whom axillary dissection may be avoided. However, patients with a positive sentinel node biopsy would require a thorough examination of their nodal status. An axillary dissection provides good local control, and accurate staging and prognostic information to inform decisions about adjuvant therapy. In addition, the survival benefit of axillary treatment is still debated. The objectives of the present study were to examine the pattern of lymph node metastases in the axilla, and evaluate the merits of a level III axillary dissection. Methods : Between June 1997 and May 2000, 308 patients underwent a total of 320 level III dissections as part of their treatment for operable invasive breast cancer. The three axillary levels were marked intraoperatively, and the contents in each level were submitted and examined separately. The patterns of axillary lymph node (ALN) metastases were examined, and factors associated with 4 positive nodes, and level III ALN metastases were evaluated by univariate and multivariate analyses. Results: An average of 25 lymph nodes were examined per case (range: 8-54), and using strict anatomical criteria, the mean numbers of ALN found in levels I, II and III were 18 (range: 2-43), 4 (range: 0 19), and 3 ( range: 0-11), respectively. Axillary lymph node involvement was found in 45% of the cases (143/320). Of the 143 cases, 78% (n = 111) had involvement of level I nodes only, and 21% (n = 30) had positive ALN in levels II and, or, III, in addition to level I. Involvement of lymph nodes in level II or III without a level I metastasis was found in two cases only (0.6%). By including level II, in addition to level I, in the dissection, four cases (1%) were converted from one to three positive nodes to 4 positive nodes (P = 0.64). By the inclusion of level III to a level I and II dissection, three cases (1%) were converted from one to three positive nodes to 4 positive nodes (P = 0.74). Involvement of lymph nodes in level III was found in 22 cases (7%), and 51 cases (16%) had 4 positive nodes. Palpability of ALN, pathological tumour size, and lymphovascular invasion (LVI), were significantly associated with level III involvement and 4 positive nodes by univariate and multivariate analyses. The frequencies of level III involvement and 4 positive nodes in patients with palpable ALN were 22% and 42%, respectively. The corresponding frequencies in patients with a clinically negative axilla, and a primary tumour which was >20 mm and LVI positive, were over 14% and 31%, respectively. Conclusion: Level III axillary dissection is appropriate for patients with palpable ALN, and in those with a tumour which is >20 mm and LVI positive, principally to reduce the risk of axillary recurrence. Staging accuracy is achieved with a level II dissection, or even a level I dissection alone based on strict anatomical criteria. Sentinel node biopsy is a promising technique in identifying pathological node-positive patients in whom an axillary clearance provides optimal local control and staging information.