Rates and Intermediates in Ser26 Mutants of Benzoylformate Decarboxylase

poster abstractBenzoylformate decarboxylase (BFDC), a thiamine diphosphate dependent enzyme, catalyzes decarboxylation of benzoylformate to benzaldehyde and CO2. The BFDC reaction proceeds through at least four individual chemical steps and, recently, NMR spectroscopy has been used to measure the ratios of intermediates in the overall reaction. This method permits calculation of rate constants for formation of the first intermediate, mandelylThDP (k2) and its subsequent decarboxylation (k3), as well as the combined breakdown of the enamine and product release (k4). As part of a study of the contributions of the active site residues, Ser26, His70 and His281, to the individual catalytic steps several Ser26 variants were expressed and purified. Initially, the variants were characterized using steady-state kinetics. Subsequently, the enzymes were mixed with benzoylformate and the mixture immediately acid quenched to trap intermediates of the reaction. NMR spectroscopy was used to identify and quantitate individual catalytic intermediates. Rate constants for the formation of these intermediates were then determined and compared to those of the wild-type enzyme. Here we report those results and discuss their implications for the role of Ser26 in the BFDC reaction mechanism

Shear flow effects on phase separation of entangled polymer blends

We introduce an entanglement model mixing rule for stress relaxation in a polymer blend to a modified Cahn-Hilliard equation of motion for concentration fluctuations in the presence of shear flow. Such an approach predicts both shear-induced mixing and demixing, depending on the relative relaxation times and plateau moduli of the two components

Phase Separation in Binary Fluid Mixtures with Continuously Ramped Temperature

We consider the demixing of a binary fluid mixture, under gravity, which is steadily driven into a two phase region by slowly ramping the temperature. We assume, as a first approximation, that the system remains spatially isothermal, and examine the interplay of two competing nonlinearities. One of these arises because the supersaturation is greatest far from the meniscus, creating inversion of the density which can lead to fluid motion; although isothermal, this is somewhat like the Benard problem (a single-phase fluid heated from below). The other is the intrinsic diffusive instability which results either in nucleation or in spinodal decomposition at large supersaturations. Experimental results on a simple binary mixture show interesting oscillations in heat capacity and optical properties for a wide range of ramp parameters. We argue that these oscillations arise under conditions where both nonlinearities are important

КЕРАМІКА КАМ’ЯНСЬКОЇ СІЧІ (1709-1711; 1728-1734 рр.): ІСТОРІЯ, ФУНКЦІОНАЛЬНІ ОСОБЛИВОСТІ, СЕМАНТИКА

Після зруйнування Чортомлицької Січі російськими військами полковника Яковлєва та козаками Гната Галаган між запорожцями та турецьким султаном Ахметом ІІІ було укладено pacta conventa. За умовами угоди при впадінні річки Кам’янки в Дніпро, вище сьогоднішнього м. Берислава (Кизикермена) запорожцями була заснована Кам’янська Січ. Топографія Січі підтверджувалася свідченням козацьких істориків ХVIII ст. С. Мишецьким, документальними джерелами із січового архіву, архіву Малоросійської колегії, дослідженнями археологічних експедицій Державного історико-культурного заповідника запорозького козацтва на о. Хортиця в 1971-1975 рр. та ін. Археологічні знахідки свідчать, що Кам’янська Січ проіснувала близько 8 років з однією тривалою перервою (1712-1728), коли Запорожці сиділи в шостій по числу – Олешківській Січі. Після трагедії на Чортомлицькій Січі новий кошовий спадкоємець героя Полтавської баталії Костя Гордієнка, енергійний і кмітливий Яків Богуш організував опір козаків Чортомлицької Січі, а потім очолив їх і заклав Кам’янську Січ

All the colours of the rainbow.

Our perception of colour has always been a source of fascination, so it's little wonder that studies of the phenomenon date back hundreds of years. What, though, can modern scientists learn from medieval literature — and how do we go about it

Unfolding dynamics of proteins under applied force

Understanding the mechanisms of protein folding is a major challenge that is being addressed effectively by collaboration between researchers in the physical and life sciences. Recently, it has become possible to mechanically unfold proteins by pulling on their two termini using local force probes such as the atomic force microscope. Here, we present data from experiments in which synthetic protein polymers designed to mimic naturally occurring polyproteins have been mechanically unfolded. For many years protein folding dynamics have been studied using chemical denaturation, and we therefore firstly discuss our mechanical unfolding data in the context of such experiments and show that the two unfolding mechanisms are not the same, at least for the proteins studied here. We also report unexpected observations that indicate a history effect in the observed unfolding forces of polymeric proteins and explain this in terms of the changing number of domains remaining to unfold and the increasing compliance of the lengthening unstructured polypeptide chain produced each time a domain unfolds

‘‘Lozenge’’ contour plots in scattering from polymer networks

We present a consistent explanation for the appearance of “lozenge” shapes in contour plots of the two dimensional scattering intensity from stretched polymer networks. By explicitly averaging over quenched variables in a tube model, we show that lozenge patterns arise as a result of chain material that is not directly deformed by the stretch. We obtain excellent agreement with experimental data