Oxidation of reduced pyridine nucleotide by a system using ascorbate and hydrogen peroxide from plants and algae

Influence of very low doses of ionizing radiation on Synechococcus lividus metabolism during the initial growth phase

Previous results from this laboratory have shown that very low chronic doses of gamma radiation can stimulate proliferation of the Cyanobacterium Synechococcus lividus. This modification of cell proliferation occurred during the first doubling. In this paper, we have compared the metabolism of cells cultivated in a normal environment or under chronic irradiation. Incubation of the cells in a new medium induced a high superoxide dismutase (EC 1.15.1.1, SOD) activity at the 18th hour and a degradation of phycocyanin, thus demonstrating that cells were submitted to a photooxidative stress. This increase in superoxide dismutase activity was followed by concomitant peaks of glutathione reductase (EC 1.6.4.2, GR) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6P-DH) at the 24th hour. Irradiated cultures at a dose of 53.5 mGray/year show an earlier and higher peak of SOD, GR, and G6P-DH. In a second stage, cultures showed an earlier onset of photosynthesis under irradiation, as evidenced by an increase in pigment content and an enhancement of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13, GAP-DH). These results show that the radiostimulation is related to the activation of enzymes protecting against peroxides that were induced under oxidative circumstances and to the activation of a glucose catabolism via the oxidative pentose phosphate pathway.

Oxidation of NAD(P)H in a Reconstituted Spinach Chloroplast Preparation Using Ascorbate and Hydrogen Peroxide

The conversion of fructose-1,6-bisphosphate to glycerate-3-phosphate (PGA) was studied in a reconstituted spinach (Spinacia oleracea L.) chloroplast preparation to determine whether a chloroplast-localized NAB(P)H-oxidizing system (Kow, Smyth, Gibbs 1982 Plant Physiol 69: 72-76 with substrates of ascorbate, NAD(P)H, and H(2)O(2) could serve as a coupling enzyme in the recycling of NAD(P)H. The rate of PGA formation was monitored as an indicator of NAD(P) generation. With NAD as a cofactor, ascorbate enhanced PGA formation, and an additional increase resulted upon addition of glucose-glucose oxidase, a H(2)O(2)-generating enzyme. This increase in PGA formation due to H(2)O(2) was eliminated by the addition of catalase. With NADP and ferredoxin as cofactors, the recycling of NADP apparently was catalyzed both by ferredoxin-NADP reductase coupled to O(2) and by the NAD(P)H-oxidizing system.It was concluded that the oxidation of NAD(P)H by a system using ascorbate and H(2)O(2) can serve as a means of recycling NAD(P)H but that another reaction involving ascorbate and NAD(P)H may also function in the spinach chloroplast.