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K562 erythroleukaemic cells produced ascorbate when incubated with dehydroascorbic acid. The reduction depended on the number of cells and on the concentration of dehydroascorbic acid. The observed rate consists of a high affinity (apparent Km 7 mu M, Vmax 3 center dot 25 pmol min-1 (10(6) cells)-1 and a low affinity component, which was non-saturable up to 1 mM of DHA (rate increase of 0 center dot 1 pmol min-1 (10(6) cells)-1 (1 mu M of DHA-1). The rate was dependent on temperature and was stimulated by glucose and inhibited by phloretin, N-ethylmaleimide, parachloro-mercuribenzoate and the noyltrifluoroacetone. Although uptake of DHA proceeded at a higher rate than its extracellular reduction, the generation of extracellular ascorbate from DHA cannot be accounted for by intracellular reduction and the release of ascorbate, since the latter was not linear with time and had an initial rate of approximately 3 pmol min-1 (10(6) cells-1). At a concentration of DHA of 100 mu M this is 25 per cent of the observed reduction.

The three-dimensional sphere-stacking PbO 2 coatings based on one-dimensional TiO 2 -NTs/Ti substrate (3D-sphere PbO 2 ) were prepared without other three-dimensional templates, only by using a simple pulse electrodeposition method. The surface morphology, compositions and crystallographic structure of 3D-sphere PbO 2 electrode were investigated fully by using the field emission scanning electron (SEM), X-ray diffractometer (XRD) and energy dispersive X-ray spectroscopy (EDX), respectively. The comparative studies between 3D-sphere PbO 2 electrode and traditional flat PbO 2 electrode (flat-PbO 2 ) indicated that the 3D-sphere PbO 2 electrode with novel structure had smaller grain size. The electrochemical performances of the 3D-sphere PbO 2 electrode were carried out by using cyclic voltammograms (CV), linear sweep voltammograms (LSV), electrochemical impedance spectroscopy (EIS) and accelerated service life, respectively. The results show that the 3D-sphere PbO 2 electrode has larger electrochemical active surface area, higher oxygen evolution potential and lower charge transfer resistance, leading to it possesses better stable service life on process of degradation than that the flat-PbO 2 electrode. Furthermore, the 3D-sphere PbO 2 electrode showed the best performance on degradation of phenol in simulated wastewater by bulk electrolysis. The removal efficiency of phenol could reach about 96.5% after 120 min under the optimal current density (30 mA cm −2 ) at room temperature, which was higher than that by using the flat-PbO 2 electrode (73.1%). In addition, the reaction rate constant (k) of 3D-sphere PbO 2 electrode degrading phenol solution was 0.0277 min −1 which was 2.56 times larger than that of flat-PbO 2 electrode (0.0108 min −1 ). Summarily, the 3D-sphere electrode is a promising electrode in treating wastewater.

K562 erythroleukaemic cells produced ascorbate when incubated with dehydroascorbic acid. The reduction depended on the number of cells and on the concentration of dehydroascorbic acid. The observed rate consists of a high affinity (apparent Km 7 mu M, Vmax 3 center dot 25 pmol min-1 (10(6) cells)-1 and a low affinity component, which was non-saturable up to 1 mM of DHA (rate increase of 0 center dot 1 pmol min-1 (10(6) cells)-1 (1 mu M of DHA-1). The rate was dependent on temperature and was stimulated by glucose and inhibited by phloretin, N-ethylmaleimide, parachloro-mercuribenzoate and the noyltrifluoroacetone. Although uptake of DHA proceeded at a higher rate than its extracellular reduction, the generation of extracellular ascorbate from DHA cannot be accounted for by intracellular reduction and the release of ascorbate, since the latter was not linear with time and had an initial rate of approximately 3 pmol min-1 (10(6) cells-1). At a concentration of DHA of 100 mu M this is 25 per cent of the observed reduction.

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