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.
Die Wirkung von Monojodessigsäure auf Atmung und Photosynthese von Chlorella
The distribution of radioactivity after feeding labeled glucose, as well as the change of the poolsize of intermediates, in Chlorella poisoned with monoiodacetic acid (MIA), showed that triosephosphate dehydrogenase is the most sensitive Enzyme in respiration. MIA leads to a large accumulation of fructose diphosphate (FDP) and a large decrease in phosphoglyceric acid (PGA). Also, the breakdown of glucose via 6-phospho-gluconate is inhibited by MIA, as shown by the small change of the C1/C6 ratio. FDP piles up during MIA poisoning in the dark and is quickly transformed to ribulose diphosphate (RuDP), in the light; subsequently, RuDP is transformed to PGA and its derivatives (pyruvate and other acids) by carboxylation and hydrolysis of the ketoacid. Thus, a third pathway of glucose breakdown, by passing glycolysis and the 6-phosphogluconate pathway, is induced by MIA in the light. The photosynthetic CO2 assimilation of Chlorella is about 100 fold more sensitive toward MIA than respiration. By feeding labeled CO2 and determining the concentration of the intermediates formed during MIA poisoning in the light, it is found that, in contrast to the behavior of broken chloroplasts, the reduction of the fixed CO2 is the most sensitive reaction of photosynthesis in Chlorella, rather than the formation of RuDP. It is assumed that the energy-rich phosphate formed in the light may be used for a relatively MIA-insensitive reaction leading to the formation of RuDP, and that the carboxylated RuDP is directly reduced to sugar by a highly ΜΙΑ-sensitive reaction. Hydrolysis to PGA occurs only if the reduction of the ketoacid proceeds too slowly, i. g., during MIA-inhibition.
EFFECTS OF AMMONIA, METHYLAMINE, AND HYDROXYLAMINE ON THE ADAPTIVE ASSIMILATION OF NITRITE AND NITRATE BY A MYCOBACTERIUM
The assimilation of nitrate and nitrite by bacteria is usually accompanied by reduction through hyponitrite and hydroxylamine to ammonium ion. Nitrate, nitrite, and hydroxylamine reductases have been isolated by Spencer et al. (1957) and Nicholas and Nason (1954). These enzymes may be either constitutive or adaptive. In the present study, it was found that washed cells of a mycobacterium assimilate nitrate and nitrite after induction of the reductases and it was thus possible to determine the effect of other nitrogenous compounds on this process.