A mechanism for NADPH inhibition of catalase compound II formation

AbstractCatalase-bound NADPH both prevents and reverses the accumulation of inactive bovine liver catalase peroxide compound II generated by ‘endogenous’ donors under conditions of steady H2O2 formation without reacting rapidly with either compound I or compound II. It thus differs both from classical 2-electron donors of the ethanol type, and from 1-electron donors of the ferrocyanide/phenol type. NADPH also inhibits compound II formation induced by the exogenous one-electron donor ferrocyanide. A catalase reaction scheme is proposed in which the initial formation of compound II from compound I involves production of a neighbouring radical species. NADPH blocks the final formation of stable compound II by reacting as a 2-electron donor to compound II and to this free radical. The proposed behaviour resembles that of labile free radicals formed in cytochrome c peroxidase and myoglobin. Such radical migration patterns within haem enzymes are increasingly common motifs

Recognizing Graph Theoretic Properties with Polynomial Ideals

Many hard combinatorial problems can be modeled by a system of polynomial equations. N. Alon coined the term polynomial method to describe the use of nonlinear polynomials when solving combinatorial problems. We continue the exploration of the polynomial method and show how the algorithmic theory of polynomial ideals can be used to detect k-colorability, unique Hamiltonicity, and automorphism rigidity of graphs. Our techniques are diverse and involve Nullstellensatz certificates, linear algebra over finite fields, Groebner bases, toric algebra, convex programming, and real algebraic geometry.Comment: 20 pages, 3 figure

Refinement of Biomarker Pentosidine Methodology for use on Aging Birds

There is no reliable method for determining age for most species of long-lived birds. Recent success using the skin chemical pentosidine as a biomarker has shown promise as an aging tool for birds. Pentosidine levels have been determined only from the breast tissue of carcasses, and we sought to refine the procedure with respect to biopsy size and location for safe and effective use on living birds. We compared pentosidine concentrations in 4 skin-size samples (4, 6, 8, and 20-mm diameter biopsies) from the breast of black vulture (Coragyps atratus) carcasses. We also compared pentosidine levels from breast and patagial tissue to document potential differences among collection sites of deceased vultures (with unknown ages) and monk parakeets (Myiopsitta monachus; with actual, minimal, and unknown ages). Pentosidine concentrations (pmol pentosidine/mg collagen) were similar among the 4 sizes of vulture breast skin (P = 0.82). Pentosidine concentrations for the breast (x̄ = 8.9, SE = 0.55, n = 28) and patagium (x̄ = 8.9, SE = 0.51, n = 28) of vultures were similar, but in parakeets, pentosidine was higher in the breast (x̄ = 15.9, SE = 1.30, n = 105) than the patagium (x̄ = 11.5, SE = 1.10, n = 105). We made pentosidine-based age estimates for vultures and parakeets using a general age curve for wild birds. We also made vulture age estimates using plumage characteristics and a cormorant (Phalacrocorax auritus) age curve. Vulture pentosidine-based age estimates appear to correspond to plumage-based age estimates. Pentosidine-based age estimates for 88% of the known-aged parakeets (n = 17) were within 6 months of actual ages. Even though known ages were not available for all birds, we found a positive trend in pentosidine versus age for both species. We suggest that 6-mm diameter skin samples from the patagium of living vultures and other similar-sized birds will provide sufficient tissue for reliable age estimation and will not impair flight ability

Statistical Inference in a Directed Network Model with Covariates

Networks are often characterized by node heterogeneity for which nodes exhibit different degrees of interaction and link homophily for which nodes sharing common features tend to associate with each other. In this paper, we propose a new directed network model to capture the former via node-specific parametrization and the latter by incorporating covariates. In particular, this model quantifies the extent of heterogeneity in terms of outgoingness and incomingness of each node by different parameters, thus allowing the number of heterogeneity parameters to be twice the number of nodes. We study the maximum likelihood estimation of the model and establish the uniform consistency and asymptotic normality of the resulting estimators. Numerical studies demonstrate our theoretical findings and a data analysis confirms the usefulness of our model.Comment: 29 pages. minor revisio

Four lectures on secant varieties

This paper is based on the first author's lectures at the 2012 University of Regina Workshop "Connections Between Algebra and Geometry". Its aim is to provide an introduction to the theory of higher secant varieties and their applications. Several references and solved exercises are also included.Comment: Lectures notes to appear in PROMS (Springer Proceedings in Mathematics & Statistics), Springer/Birkhause

Depicting the tree of life: The philosophical and historical roots of evolutionary tree diagrams

info:eu-repo/semantics/publishedVersio

Rank Analysis of Cubic Multivariate Cryptosystems

In this work we analyze the security of cubic cryptographic constructions with respect to rank weakness. We detail how to extend the big field idea from quadratic to cubic, and show that the same rank defect occurs. We extend the min-rank problem and propose an algorithm to solve it in this setting. We show that for fixed small rank, the complexity is even lower than for the quadratic case. However, the rank of a cubic polynomial in $n$ variables can be larger than $n$, and in this case the algorithm is very inefficient. We show that the rank of the differential is not necessarily smaller, rendering this line of attack useless if the rank is large enough. Similarly, the algebraic attack is exponential in the rank, thus useless for high rank

INTERSPECIES COMPARISON OF PENTOSIDINE ACCUMULATION AND ITS CORRELATION WITH AGE IN BIRDS

Recent studies suggest that a linear correlation exists between the age of individual birds and accumulation of the advanced glycation endproduct pentosidine (Ps). We compared Ps accumulation in skin tissue of Ruffed Grouse (Bonasa umbellus) and Double-crested Cormorants (Phalacrocorax auritus). Skin samples were taken from the breasts of 52 Ruffed Grouse of known ages ranging from a few days to 10 years. Skin was cleaned of feathers and adipose tissue, acid hydrolyzed, and measured for collagen content via hydroxyproline spectrophotometric assay. Pentosidine concentrations were determined using reverse-phase high-performance liquid chromatography. Fluorescent detection (excitation: 310 nm, emission: 385 nm) revealed that concentrations of Ps per milligram of collagen increased curvilinearly with age (r2 = 0.87, P \u3c 0.0001). Additionally, a blind study of 19 Double-crested Cormorants revealed a linear relationship between Ps concentrations and age (r2 = 0.93). Comparison of these two species revealed a more rapid accumulation of Ps in Ruffed Grouse. Accurate age information could aid species recovery programs and provide insights into longevity, now understood entirely from banding programs and captive birds

A systems approach to architecting a mission package for LCS support of amphibious operations

The United States Navy andMarine Corps have identified capability gaps in the areas of collecting Intelligence, Surveillance, Reconnaissance, and Targeting (ISR&T) data and employing fires during amphibious operations. The Littoral Combat Ship (LCS) presents an opportunity to deploy specific mission capabilities in the amphibious theater. This paper identifies the operational, functional, and physical architecture of an LCS Amphibious Warfare Mission Package (LAMP) necessary to provide capabilities associated with ISR&T data collect and fires employment. Physical architecture configurations are evaluated using a discrete-event model. Cost estimates for each alternative are presented in order to identify the LAMP architecture that provides the most cost-effective solution for providing capabilities associated with ISR&T data collection and fires employment. This paper concludes by identifying potential LAMP assets that would provide cost-effective support of amphibious operations. Four feasible alternatives are ultimately identified as cost-effective solutions, with LCCEs ranging from $105.49M and$188.22M and providing varying levels of effectiveness in terms of average engagement time and percentage of threats successfully affected.http://archive.org/details/asystemspproacht1094543992Approved for public release; distribution is unlimited