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Metabolism of oxygen radicals in peroxisomes and cellular implications

Peroxisomes are subcellular respiratory organelles which contain catalase and H2O2-producing flavin oxidases as basic enzymatic constituents. These organelles have an essentially oxidative type of metabolism and have the potential to carry out different important metabolic pathways. In recent years the presence of different types of superoxide dismutase (SOD) have been demonstrated in peroxisomes from several plant species, and more recently the occurrence of SOD has been extended to peroxisomes from human and transformed yeast cells. A copper,zinc-containing SOD from plant peroxisomes has been purified and partially characterized. The production of hydroxyl and superoxide radicals has been studied in peroxisomes. There are two sites of O2- production in peroxisomes: (1) in the matrix, the generating system being xanthine oxidase; and (2) in peroxisomal membranes, dependent on reduced nicotinamide adenine dinucleotide (NADH), and the electron transport components of the peroxisomal membrane are possibly responsible. The generation of oxygen radicals in peroxisomes could have important effects on cellular metabolism. Diverse cellular implications of oxyradical metabolism in peroxisomes are discussed in relation to phenomena such as cell injury, peroxisomal genetic diseases, peroxisome proliferation and oxidative stress, metal and salt stress, catabolism of nucleic acids, senescence, and plant pathogenic processes.

Peroxisomal Copper,Zinc Superoxide Dismutase (Characterization of the Isoenzyme from Watermelon Cotyledons)

The biochemical and immunochemical characterization of a superoxide dismutase (SOD, EC 1.15.1.1) from peroxisomal origin has been carried out. The enzyme is a Cu,Zn-containing SOD (CuZn-SOD) located in the matrix of peroxisomes from watermelon (Citrullus vulgaris Schrad.) cotyledons (L.M. Sandalio and L.A. del Rio [1988] Plant Physiol 88: 1215–1218). The amino acid composition of the enzyme was determined. Analysis by reversed-phase high-performance liquid chromatography of the peroxisomal CuZn-SOD incubated with 6 M guanidine-HCI indicated that this enzyme contained a noncovalently bound chromophore group that was responsible for the absorbance peak of the native enzyme at 260 nm. The amino acid sequence of the peroxisomal CuZn-SOD was determined by Edman degradation. Comparison of its sequence with those reported for other plant SODs revealed homologies of about 70% with cytosolic CuZn-SODs and of 90% with chloroplastic CuZn-SODs. The peroxisomal SOD has a high thermal stability and resistance to inactivation by hydrogen peroxide. A polyclonal antibody was raised against peroxisomal CuZn-SOD, and by western blotting the antibody cross-reacted with plant CuZn-SODs but did not recognize either plant Mn-SOD or bacterial Fe-SOD. The antiSOD-immunoglobulin G showed a weak cross-reaction with bovine erythrocytes and liver CuZn-SODs, and also with cell-free extracts from trout liver. The possible function of this CuZn-SOD in the oxidative metabolism of peroxisomes is discussed.

Induction of catalase and ascorbate peroxidase activities in tobacco roots inoculated with the arbuscular mycorrhizal Glomus mosseae

Catalase and ascorbate peroxidase enzymatic activities were examined during the interaction between Nicotiana tabacum and the arbuscular mycorrhizal Glomus mosseae. Transient enhancements of both enzymatic activities were detected in the inoculated plant roots coinciding in time with the stage of appressoria formation in the root surface. The analysis of free salicylic acid content in roots revealed that the increases in enzymatic activities were coincident in time with the accumulation of SA in inoculated roots. These data indicate that the first reaction of the root cells to the invasion of arbuscular mycorrhizal fungi is a defence response.

Changes induced by NaCl in lipid content and composition, lipoxygenase, plasma membrane H+-ATPase and antioxidant enzyme activities of tomato (Lycopersicon esculentum. Mill) calli

Tomato (Lycopersicon esculentum Mill. cv. Pera) calli tolerant to 50 mM NaCl were obtained by successive subcultures in NaCl supplemented medium. Salt-tolerant calli showed an increase of fresh and dry weight respective to control calli. When control and 50 mM NaCl-tolerant calli were stressed with 100 mM NaCl for 48 h, a decrease in respiration rate of 32 and 9%, respectively, was observed. Relative proportions of phospholipid fatty acids and free-sterol molecular species were the same in both control and NaCl tolerant calli. While the content of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased in salt-tolerant calli, the free sterol content was similar in both cases. A substantial increase of vanadate-sensitive ATP-dependent H+ pumping activity without any modification in specific phosphohydrolytic activity and in passive H+ conductance was detected in microsomes from salt-tolerant calli, which could be explained by an increased coupling between H+ pumping and ATP hydrolysis. The higher lipoxygenase and antioxidant enzyme activities such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and glutathione-S-transferase in 50 mM NaCl-tolerant calli as compared to controls also suggest that salt-tolerant calli has a high capacity of polyunsaturated fatty acid hydroperoxide formation and active oxygen species scavenging.

Universality of Corner Entanglement in Conformal Field Theories

We study the contribution to the entanglement entropy of (2+1)-dimensional conformal field theories (CFTs) coming from a sharp corner in the entangling surface. This contribution is encoded in a function a(θ) of the corner opening angle, and was recently proposed as a measure of the degrees of freedom in the underlying CFT. We show that the ratio a(θ)/C(T), where C(T) is the central charge in the stress tensor correlator, is an almost universal quantity for a broad class of theories including various higher-curvature holographic models, free scalars, and fermions, and Wilson-Fisher fixed points of the O(N) models with N=1,2,3. Strikingly, the agreement between these different theories becomes exact in the limit θ→π, where the entangling surface approaches a smooth curve. We thus conjecture that the corresponding ratio is universal for general CFTs in three dimensions.

Corner contributions to holographic entanglement entropy

A bstractThe entanglement entropy of three-dimensional conformal field theories contains a universal contribution coming from corners in the entangling surface. We study these contributions in a holographic framework and, in particular, we consider the effects of higher curvature interactions in the bulk gravity theory. We find that for all of our holographic models, the corner contribution is only modified by an overall factor but the functional dependence on the opening angle is not modified by the new gravitational interactions. We also compare the dependence of the corner term on the new gravitational couplings to that for a number of other physical quantities, and we show that the ratio of the corner contribution over the central charge appearing in the two-point function of the stress tensor is a universal function for all of the holographic theories studied here. Comparing this holographic result to the analogous functions for free CFT’s, we find fairly good agreement across the full range of the opening angle. However, there is a precise match in the limit where the entangling surface becomes smooth, i.e., the angle approaches π, and we conjecture the corresponding ratio is a universal constant for all three-dimensional conformal field theories. In this paper, we expand on the holographic calculations in our previous letter arXiv:1505.04804, where this conjecture was first introduced.

IMMUNOCYTOCHEMICAL LOCALIZATION OF COPPER, ZINC SUPEROXIDE DISMUTASE IN PEROXISOMES FROM WATERMELON (CITRULLUS VULGARIS SCHRAD.) COTYLEDONS

In previous works using cell fractionation methods we demonstrated the presence of a Cu,Zn-containing superoxide dismutase in peroxisomes from watermelon cotyledons. In this work, this intracellular localization was evaluated by using western blot and EM immunocytochemical analysis with a polyclonal antibody against peroxisomal Cu,Zn-SOD II from watermelon cotyledons. In crude extracts from 6-day old cotyledons, analysis by western blot showed two cross-reactivity bands which belonged to the isozymes Cu,Zn-SOD I and Cu,Zn-SOD II. In peroxisomes purified by sucrose density-gradient centrifugation only one cross-reactivity band was found in the peroxisomal matrix which corresponded to the isozyme Cu,Zn-SOD II. When SOD activity was assayed in purified peroxisomes two isozymes were detected, Cu,Zn-SOD II in the matrix, and a Mn-SOD in the membrane fraction which was removed by sodium carbonate washing. EM immunocytochemistry of Cu,Zn-SOD on sections of 6-day old cotyledons, showed that gold label was mainly localized over plastids and also in peroxisomes and the cytosol, whereas mitochondria did not label for Cu,Zn-SOD.

Lifshitz-like solutions with hyperscaling violation in ungauged supergravity

A bstractIn this note we describe several procedures to construct, from known black-hole and black-brane solutions of any ungauged supergravity theory, non-trivial gravitational solutions whose “near-horizon” and “near-singularity” limits are Lifshitz-like spacetimes with dynamical critical exponent z, “hyperscaling violation” exponent θ and Lifshitz radius ℓ that depends on the physical parameters of the original black-hole solution. Since the new Lifshitz-like solutions can be constructed from any black-hole solution of any ungauged supergravity, many of them can be easily embedded in String Theory. Some of the procedures produce supersymmetric Lifshitz-like solutions.

Universal corner entanglement from twist operators

A bstractThe entanglement entropy in three-dimensional conformal field theories (CFTs) receives a logarithmic contribution characterized by a regulator-independent function a(θ) when the entangling surface contains a sharp corner with opening angle θ. In the limit of a smooth surface (θ → π), this corner contribution vanishes as a(θ) = σ(θ − π)2. In arXiv:1505.04804, we provided evidence for the conjecture that for any d = 3 CFT, this corner coefficient σ is determined by CT, the coefficient appearing in the two-point function of the stress tensor. Here, we argue that this is an instance of a much more general relation connecting the analogous corner coefficient σn appearing in the nth Rényi entropy and the scaling dimension hn of the corresponding twist operator. In particular, we find the simple relation hn/σn = (n − 1)π. We show how it reduces to our previous result as n → 1, and explicitly check its validity for free scalars and fermions. With this new relation, we show that as n → 0, σn yields the coefficient of the thermal entropy, cS. We also reveal a surprising duality relating the corner coefficients of the scalar and the fermion. Further, we use our result to predict σn for holographic CFTs dual to four-dimensional Einstein gravity. Our findings generalize to other dimensions, and we emphasize the connection to the interval Rényi entropies of d = 2 CFTs.

Universal entanglement for higher dimensional cones

A bstractThe entanglement entropy of a generic d-dimensional conformal field theory receives a regulator independent contribution when the entangling surface contains a (hyper)conical singularity of opening angle Ω, codified in a function a(d)(Ω). In arXiv:1505.04804, we proposed that for three-dimensional conformal field theories, the coefficient σ(3) characterizing the limit where the surface becomes smooth is proportional to the central charge CT appearing in the two-point function of the stress tensor. In this paper, we prove this relation for general three-dimensional holographic theories, and extend the result to general dimensions. In particular, we define a generalized coefficient σ(d) to characterize the almost smooth limit of a (hyper)conical singularity in entangling surfaces in higher dimensions. We show then that this coefficient is universally related to CT for general holographic theories and provide a general formula for the ratio σ(d)/CT in arbitrary dimensions. We conjecture that the latter ratio is universal for general CFTs. Further, based on our recent results in arXiv:1507.06997, we propose an extension of this relation to general Rényi entropies, which we show passes several consistency checks in d = 4 and 6.