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.
CLINICAL TRIALS OF THE ABDOMINAL LEFT VENTRICULAR ASSIST DEVICE (ALVAD): PROGRESS REPORT.
An abdominal left ventricular assist device (ALVAD) is undergoing controlled clinical trials in our institution. The ALVAD is pneumatically-actuated, synchronously or asynchronously with an external console and is interposed between the apex of the left ventricle and the infrarenal abdominal aorta. It is an order of magnitude more effective than conventional intraaortic balloon pumping. Thus far, we have implanted this pump in 21 patients (15 males and six females). The average age has been 50. The duration of cardiopulmonary bypass with intensive pharmacologic support and IABP until ALVAD implantation has been nearly 4 hours. The plasma hemoglobins prior to ALVAD implantation have averaged 168 mg%. The platelet counts at implantation have averaged 68,000 mm(3). The average duration of ALVAD support has been in excess of one day and the longest trial extended for one week. We have been able to remove the pump after ventricular recovery in two instances and effected cardiac allografting in one instance of ALVAD dependency. We have found that (1) the profoundly depressed left (and right) ventricles can recover if totally supported with this device; (2) the device can function in the presence of ventricular fibrillation and/or standstill; (3) the device can effectively replace both left and right ventricular function in the presence of normal pulmonary vascular resistance and microcirculatory hemodynamics; and (4) in the presence of impending multiple organ failure, procrastination in use is to be avoided.