CaII Binding Regulates and Dominates the Reactivity of a Transition‐Metal‐Ion‐Dependent Diesterase from Mycobacterium tuberculosis

The diesterase Rv0805 from Mycobacterium tuberculosis is a dinuclear metallohydrolase that plays an important role in signal transduction by controlling the intracellular levels of cyclic nucleotides. As Rv0805 is essential for mycobacterial growth it is a promising new target for the development of chemotherapeutics to treat tuberculosis. The in vivo metal‐ion composition of Rv0805 is subject to debate. Here, we demonstrate that the active site accommodates two divalent transition metal ions with binding affinities ranging from approximately 50 nm for Mn^II to about 600 nm for Zn^II. In contrast, the enzyme GpdQ from Enterobacter aerogenes, despite having a coordination sphere identical to that of Rv0805, binds only one metal ion in the absence of substrate, thus demonstrating the significance of the outer sphere to modulate metal‐ion binding and enzymatic reactivity. Ca^II also binds tightly to Rv0805 (K_d≈40 nm ), but kinetic, calorimetric, and spectroscopic data indicate that two Ca^II ions bind at a site different from the dinuclear transition‐metal‐ion binding site. Ca^II acts as an activator of the enzymatic activity but is able to promote the hydrolysis of substrates even in the absence of transition‐metal ions, thus providing an effective strategy for the regulation of the enzymatic activity.     

Set-indexed Brownian Motion on Increasing Paths

We prove that a square-integrable set-indexed stochastic process is a set-indexed Brownian motion if and only if its projections on all the strict increasing continuous paths are one-parameter time-change Brownian motions. We present some applications.     

Thiol–norbornene materials: Approaches to develop high Tg thiol–ene polymers

The ability to prepare high T_g low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (T_g) for several thiol–norbornene materials. Results indicate that T_gs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high T_g materials. In particular, as much as a 70 °C increase in T_g was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007     

A martingale characterization of the set-indexed Brownian motion

We characterize a Brownian motion indexed by a semilattice of sets, using the theory of set-indexed martingales: a square integrable continuous set-indexed strong martingale is a Brownian motion if and only if its compensator is deterministic and continuous.Research supported by a grant from the Natural Sciences and Engineering Research Council of Canada.Research done while this author was visiting the University of Ottawa. He wishes to thank Professor Ivanoff for her kind hospitality.     

Unorthodox intrasubunit interactions in the cellulosome ofClostridium thermocellum

Clostridium thermocellum, an anaerobic thermophilic cellulolytic bacterium, produces an extremely cohesive, very high-molecular-mass multicellulase-containing complex termed thecellulosome. One of its components, the S1 subunit, is a nonenzymatic, 210 kDa glycopolypeptide. Upon preconditioning of the intact cellulosome with lowionic-strength or low-pH solutions, the S1 subunit separates in hot sodium dodecyl sulfate (SDS) solutions into a series of defined lowermolecular-mass subcomponents. Under the same conditions, the purified S1 subunit demonstrated the same behavior. Higher levels of glycosylation associated with the larger S1 subcomponents. The data support alterations in the conformational state of the S1 structure that lead to its disintegration induced by combined treatments with SDS and heating. Evidence is provided that this phenomenon may reflect a physiological response of the cellulosome, since similar alterations in S1 appear to accompany its binding to cellulose.     

A study of transverse and longitudinal momentum correlations in proton diffraction dissociation at 14 GeV/c

We present data on momentum correlations both in and out of the production plane for the reactions π⁺p→π_f⁺(π⁺n) and π^?p→π_f^?(π^?Δ⁺⁺). The dissociation products show strikingly similar transverse momentum distributions which in terms of exchange models suggest an equal amount of pion and baryon exchange. For both reactions, we find an approximate factorization in the projectile frame between the transverse momentum of π_f and the longitudinal momenta of the dissociation products. Exchange models predict this result equally in both reactions, but it appears much more clearly in the Δ reaction. Finally, we relate the observed longitudinal and transverse momentum distributions in a way suggested by an isotropic decay model.     

Stopping for two-dimensional stochastic processes

The aim of this paper is to introduce some techniques that can be used in the study of stochastic processes which have as parameter set the positive quadrant of the plane R²₊. We define stopping lines and derive an interesting property of measurability for them. The notion of predictability is developed, and we show the connection between predictable processes, fields associated with stopping lines, and predictable stopping lines. We also give a theorem of section for predictable sets. Extension to processes indexed by any partially ordered set with some regularity assumptions can be carried out quite easily with the same techniques.