Intrusive Traits of Victor Chikezie Uchendu

Reflections of a former student and colleague of Professor Victor Chikezie Uchendu, author of The Igbo of South East Nigeria. This tribute reflects on his major contributions to knowledge and what a loss that the academic community suffered at the hands of his assassins.     

Lignin degradeation by white rot fungi

Abstract. The wood-degrading white-rot fungus Phanerochaete chrysosporium , has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin.     

Scavenging of superoxide radical by ascorbic acid

Using acetaldehyde and xanthine oxidase as the source of suPeroxide radical, the second order rate constant for the reaction between ascorbic acid and superoxide radical was estimated to be 8.2 X 10⁷ M^-1 s^-1. In rats, the average tissue concentration of ascorbic acid was of the order of 10^-3 M and that of superoxide dismutase was of the order of 10^-6 M. So, taking together both the rate constants and the tissue concentrations, the efficacy of ascorbic acid for scavenging superoxide radical in animal tissues appears to be better than that of suPeroxide dismutase. The significance of ascorbic acid as a scavenger of superoxide radical has been discussed from the point of view of the evolution of ascorbic acid synthesizing capacity of terrestrial vertebrates.     

Mutations by near-ultraviolet radiation in Escherichia coli strains lacking superoxide dismutase

Om wild-type Escherichia coli, near-ultraviolet radiation (NUV) was only weakly mutagenic. However, in an allelic mutant strain (sodA sodB) that lacks both Mn- and Fe-superoxide dismutase (SOD) and assumed to have excess superoxide anion (O₂⁻), NUV induced a 9-fold increase in mutation above the level that normally occurs in this double mutant. When a sodA sodB double mutant contained a plasmid carrying katG⁺ HP-I catalase), mutation by NUV was reduced to wild-type (sodA⁺ sodB⁺) levels. Also, in the sodA sodB xthA triple mutant, which lacks exonuclease III (exoIII) in addition to SOD, the mutations frequency by NUV was reduced to wild-type levels. This synergistic action of NUV and O₂⁻ suggested that pre-mutational lesions occur, with exoIII converting these lesions to stable mutants. Exposure to H₂O₂ induced a 2.8 fold increase in mutations in sodA sodB double mutants, but was reduced to control levels when a plasmid carrying katG⁺ was introduced. These results suggest that NUV, in addition to its other effects on cells, increases mutations indirectly by increasing the flux of OH^. radicals, possibly by generating excess H₂O₂.     

Mn2+ reduces Yz + in manganese-depleted Photosystem II preparations

Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn²⁺. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Y_z ⁺, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Y_z ⁺ reduction by benzidine was a linear function of benzidine concentration. The rate of Y_z ⁺ reduction by Mn²⁺ at pH 6 increased linearly at low Mn²⁺ concentrations and reached a maximum at the Mn²⁺ concentrations equal to several times the reaction center concentration. The rate was inhibited by K⁺, Ca²⁺ and Mg²⁺. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Y_z ⁺ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn²⁺ near Y_z ⁺ at a site that may be one of the native manganese binding sites.Abbreviations PS II Photosystem II - Y_D tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum - Y_z tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation - ESR electron spin resonance - DPC diphenylcarbazide - DCIP dichlorophenolindophenol     

Alterations in cardiac membrane Ca2+ transport during oxidative stress

Although cardiac dysfunction due to ischemia-reperfusion injury is considered to involve oxygen free radicals, the exact manner by which this oxidative stress affects the myocardium is not clear. As the occurrence of intracellular Ca²⁺ overload has been shown to play a critical role in the genesis of cellular damage due to ischemia-reperfusion, this study was undertaken to examine whether oxygen free radicals are involved in altering the sarcolemmal Ca²⁺-transport activities due to reperfusion injury. When isolated rat hearts were made globally ischemic for 30 min and then reperfused for 5 min, the Ca²⁺ -pump and Na⁺-Ca²⁺ exchange activities were depressed in the purified sarcolemmal fraction; these alterations were prevented when a free radical scavenger enzymes (superoxide dismutase plus catalase) were added to the reperfusion medium. Both the Ca²⁺- pump and Na⁺- Ca²⁺ exchange activities in control heart sarcolemmal preparations were depressed by activated oxygen-generating systems containing xanthine plus xanthine oxidase and H₂O₂; these changes were prevented by the inclusion of superoxide dismutase and catalase in the incubation medium. These results support the view that oxidative stress during ischemia-reperfusion may contribute towards the occurrence of intracellular Ca²⁺ overload and subsequent cell damage by depressing the sarcolemmal mechanisms governing the efflux of Ca²⁺ from the cardiac cell.     

Superoxide scavenging activity of BG-104 before and after sonication-determined by ESR spin trapping method

BG-104 is a compound of Chinese herbs which were treated with infrared ray-heating and brewed with microorganisms resulting in activation of actual principles contained in the herbs, and its effectiveness has been reported on various inflammatory disorders such as Behcet's disease, rheumatoid arthritis, bacterial infections and so on. In addition, it is noted as an effective agent to retard cancer progress. This report shows a superoxide scavenging activity of BG-104 using an ESR spin trapping method. For the measurement of superoxide scavenging activity, recombinant human superoxide dismutase is used as a standard. Superoxide scavenging activity of BG-104 increases in a dose-dependent manner and activity is significantly augmented by its sonication.     

植物单盐毒害和离子拮抗机理研究Ⅰ.单盐和混合盐对植物原生质体膜某些特性、超氧物歧化酶和过氧化氢酶活性的影响

单盐(KCl, CaCl_2或MgCl_2)和混合盐(KC_1+CaCl_2或KCl+MgCl_2)对植物原生质体完整率、存活率和膜透性等均有明显影响。K~+、Ca~(2+)或Mg~(2+)等单种阳离子明显降低原生质体膜完整率和存活率而增加其物质渗漏量,其中以单价阳离子K~+的影响为甚。上述单种阳离子还明显降低小麦幼叶超氧物歧化酶(SOD)和过氧化氢酶活性。只有由单价和二价阳离子组成的平衡混合盐才能使原生质体维持较高的完整率、存活率和较正常的膜透性.并能使细胞维持较高的SOD和过氧化氢酶活性。 认为单盐毒害机理可能是首先引起细胞膜发生不正常的膜相变或细胞累积较多的有害氧自由基,引起膜脂发生过氧化或脱酯化而破坏膜结构。在离子平衡混合盐作用下,膜系才能维持正常液晶相,具有较高活性的SOD和过氧化氢酶等生物保护性酶系是离子拮抗作用之原因。