Untersuchungen zur lichtabhängigen Nitritreduktion von Chlorella
Summary1.The dependence of nitrite reduction activity in Chlorella fuscaShihira et Krauss, as measured by uptake of nitrite, on the developmental stage, light intensity and CO2 concentration was investigated.2.There is a quantitative relation between uptake of nitrite-nitrogen and increase of organic cell-nitrogen.3.The kinetics of nitrite reduction in light are linear with time at high CO2 concentrations (3% in air) but biphasic at low CO2 concentrations (0 to 0.03%). In the steady state phase nitrite uptake is stimulated by an increase in the CO2 concentration from 0 to 0.03%. The initial phase and the steady state phase exhibit a different temperature dependence.4.Nitrite uptake in the steady state phase is completely inhibited by iodoacetamide at concentrations which inhibit the photosynthetic CO2 reduction (5×10−5 M). At lower iodoacetamide concentrations (1 to 2×10−5 M) the linear time course of nitrite uptake at high CO2 concentrations is changed in the same manner as it is when the CO2 concentration is lowered.It is concluded that under special conditions (e.g. low CO2 concentration) the rate of steady state nitrite reduction in light is limited by the supply of carbon skeleton (i.e. N acceptors in the synthesis of organic nitrogen compounds) from the photosynthetic CO2 reduction cycle.5.Pre-illumination in the presence of nitrite followed by a dark period depresses the initial phase of nitrite uptake in light at low CO2 concentrations. Pretreatment with nitrite in the dark lowers the nitrite uptake of the cells in the initial phase by exactly the same amount of nitrite which has been taken up during the pre-darkening period.
 It is concluded that there is a correlation between the initial phase of nitrite reduction in light and the respiration-linked nitrite reduction in the dark.
Nitrite Reduction by Isolated Chloroplasts in Light
Losada, Whatley and Arnon1 have shown that non-cyclic photo-phosphorylation in chloroplasts is the result of two independent light reactions: (a) a photo-oxidation of water, which is absent in photosynthetic bacteria; (b) a non-cyclic photo-phosphorylation of the bacterial type2. By inhibiting1 or destroying3 the system involved in the photo-oxidation of water, it has been possible to couple the light-dependent oxidation of certain suitable electron donors (ascorbate, cystein) with the photoreduction of such low-potential electron carriers as methyl or benzyl viologen4. These artificial co-factors can be used with the aid of bacterial hydrogenase either for the fixation or for the dark and light evolution of hydrogen gas2,4,5. Mortenson et al.6 and Paneque and Arnon3 have shown that ferredoxin is the natural electron transferring factor involved in these reactions. According to Tagawa and Arnon7, the pyridine nucleotide reducing factors previously isolated and purified from either green plants8,9 or photosynthetic bacteria1 are ferredoxins.
Enzymes of Inorganic Nitrogen Metabolism
The enzymes considered in this chapter include nitrate reductase, nitrite reductase, hyponitrite reductase, hydroxylamine reductase, enzymes of denitrification, and some other enzymes such as aldehyde oxidase with related properties. The properties of the various enzymes are described in relation to the different plants and micro-organisms from which they have been obtained1.