Leopold Flohé

Bio: Leopold Flohé is an academic researcher from University of the Republic. The author has contributed to research in topics: Peroxidase & Glutathione peroxidase. The author has an hindex of 67, co-authored 198 publications receiving 20607 citations. Previous affiliations of Leopold Flohé include Braunschweig University of Technology & University of Pennsylvania.

Assays of glutathione peroxidase

Abstract: Publisher Summary To determine glutathione peroxidase reliably, some factors of potential pitfall have to be considered, for example, enzymatic side reactions of substrates (especially when crude tissue samples are assayed), high and variable spontaneous reaction rates of substrates, and the peculiar kinetics of the enzyme itself. With the best documented example, the enzyme of bovine red blood cells, ping-pong kinetics with infinite limiting maximum velocities, and Michaelis constants have been established. This means that the generally recommended conditions for determination of enzyme activity––that is, “saturating” concentrations of all substrates, cannot possibly be fulfilled. In consequence, compromises are inevitable in the choice of substrate concentration for the assay and in the definition of the unit of activity. Fixed-time assay measuring H 2 O 2 consumption and continuous monitoring of Glutathione disulfide (GSSG) formation are cited here. The main differences between the assay procedure described and those proposed by others are listed in the chapter. To compare the results obtained by different procedures, appropriate empirical converting factors are also given.

Dual Function of the Selenoprotein PHGPx During Sperm Maturation

Abstract: The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) changes its physical characteristics and biological functions during sperm maturation PHGPx exists as a soluble peroxidase in spermatids but persists in mature spermatozoa as an enzymatically inactive, oxidatively cross-linked, insoluble protein In the midpiece of mature spermatozoa, PHGPx protein represents at least 50 percent of the capsule material that embeds the helix of mitochondria The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency

Diversity of glutathione peroxidases.

Abstract: Publisher Summary This chapter focuses on the diversity of glutathione peroxidases Selenium was identified as a toxic factor for grazing animals in the first half of the twentieth century and since then has been considered hazardous Only long after the identification of the first selenoenzymes in bacteria and mammals was a Recommended Dietary Allowance gradually established In fact, the putative biological roles of the selenoenzymes, particularly those of the glutathione peroxidases (GPX), proved instrumental in the understanding of selenium deficiency syndromes in livestock and humans, although the emerging complexity of selenium enzymology still precludes definitive conclusions The selenium-dependent peroxidases have long been considered a late achievement of evolution, as they were only detected in vertebrates This view now has to be revised Whether the common ancester of the GPX superfamily was a selenoprotein or a cysteine-containing homolog cannot be deduced from the available sequences The only prokaryotic member of the superfamily detected so far, a cobalamine-binding protein of Escherichia coli , does not contain selenocysteine, and despite ongoing efforts, functionally active glutathione peroxidases have not yet been found in prokaryotes

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Free Radicals in the Physiological Control of Cell Function

Abstract: At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, how...

Involvement of the Superoxide Anion Radical in the Autoxidation of Pyrogallol and a Convenient Assay for Superoxide Dismutase

Abstract: The autoxidation of pyrogallol was investigated in the presence of EDTA in the pH range 7.9–10.6. The rate of autoxidation increases with increasing pH. At pH 7.9 the reaction is inhibited to 99% by superoxide dismutase, indicating an almost total dependence on the participation of the superoxide anion radical, O2·−, in the reaction. Up to pH 9.1 the reaction is still inhibited to over 90% by superoxide dismutase, but at higher alkalinity, O2·− -independent mechanisms rapidly become dominant. Catalase has no effect on the autoxidation but decreases the oxygen consumption by half, showing that H2O2 is the stable product of oxygen and that H2O2 is not involved in the autoxidation mechanism. A simple and rapid method for the assay of superoxide dismutase is described, based on the ability of the enzyme to inhibit the autoxidation of pyrogallol. A plausible explanation is given for the non-competitive part of the inhibition of catechol O-methyltransferase brought about by pyrogallol.

How mitochondria produce reactive oxygen species.

Abstract: The production of ROS (reactive oxygen species) by mammalian mitochondria is important because it underlies oxidative damage in many pathologies and contributes to retrograde redox signalling from the organelle to the cytosol and nucleus. Superoxide (O2•−) is the proximal mitochondrial ROS, and in the present review I outline the principles that govern O2•− production within the matrix of mammalian mitochondria. The flux of O2•− is related to the concentration of potential electron donors, the local concentration of O2 and the second-order rate constants for the reactions between them. Two modes of operation by isolated mitochondria result in significant O2•− production, predominantly from complex I: (i) when the mitochondria are not making ATP and consequently have a high Δp (protonmotive force) and a reduced CoQ (coenzyme Q) pool; and (ii) when there is a high NADH/NAD+ ratio in the mitochondrial matrix. For mitochondria that are actively making ATP, and consequently have a lower Δp and NADH/NAD+ ratio, the extent of O2•− production is far lower. The generation of O2•− within the mitochondrial matrix depends critically on Δp, the NADH/NAD+ and CoQH2/CoQ ratios and the local O2 concentration, which are all highly variable and difficult to measure in vivo. Consequently, it is not possible to estimate O2•− generation by mitochondria in vivo from O2•−-production rates by isolated mitochondria, and such extrapolations in the literature are misleading. Even so, the description outlined here facilitates the understanding of factors that favour mitochondrial ROS production. There is a clear need to develop better methods to measure mitochondrial O2•− and H2O2 formation in vivo, as uncertainty about these values hampers studies on the role of mitochondrial ROS in pathological oxidative damage and redox signalling.