Influence of Organic-Phosphates on 3-Phosphoglycerate Dependent O2 Evolution in C3 and C4 Mesophyll Chloroplasts

In C₄ plants phosphoenolpyruvate (PEP) of the C₄ cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C₃ plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O₂ evolution by C₄ (Digitaria sanquinalisL. Scop.) and C₃ (Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C₄ mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (K_i = 2.1 mM) of 3-PGA dependentO₂ evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (K_t= 8.6 mM) of O₂ evolution in the C₄ mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO₂ evolution in the C₃ chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O₂2 evolutionin both chloroplast types. The selectivity in inhibition ofO₂ evolution with 3-PGA as substrate suggests that the C₄ mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C₄ mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C₄ mesophyll chloroplasts. ¹ Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987)     

The biological action of low-level radiation

On the basis of their own data and the literature the authors have analyzed the mechanism of biological action of low-level radiation on cells. In studying the harmful effect of gamma-radiation (10-40 cGy) on HeLa cells it was shown that damages occurred in 12 postirradiation generations. Analysis of cell distribution within the colonies has demonstrated that the share of colonies with low cell content and the number of giant cell increase. These data indicate that low-level radiation causes reproductive cell death that can occur not immediately but in later generations.     

Dynorphin A [1-17] induces "reward" in rats in the place conditioning paradigm

Intracerebroventricular (i.c.v.) administration of dynorphin A [1-17] induced significant place preference conditioning in male, Sprague-Dawley rats. Place preferences were induced by 2.3 and 3.5 nmole, but not 1.2 nmole of dynorphin A. Co-administration of naloxone, 27.5 nmole but not 5.5 nmole, antagonized the reward response induced by 2.3 nmole of dynorphin A. Leu-enkephalin, 5 or 25 nmole, and dynorphin A [2-17], 2.3 or 3.5 nmole, had no effect in the place conditioning paradigm.     

The effect of administering corticoliberin into the striatum on the open-field and shuttle-box behaviors of KHA and KLA strain rats]

The effects of corticotropin-releasing hormone (CRH) injected into the dorsal neostriatum on the open-field and shuttle-box behavior were studied in rats with high (Koltushi high avoidance, KHA) and low (Koltushi low avoidance, KLA) capability for avoidance learning. The effects of this hormone on the behavior of these rat strains were different. In KLA rats with passive strategy of behavior the CRH injection led to a rapid locomotor activation in the open field, while the rats with active behavioral strategy (KHA) reacted to the injection by a significant decrease in locomotion and change for the passive mode of behavior. The same CRH effects on locomotion were obtained in the shuttle-box experiments. Moreover, in the KLA rats the neurohormone injection resulted in an improvement of avoidance learning in contrast to the KHA rats, in which CRH substantially impaired avoidance learning. The obtained evidence is discussed in terms of the important role of striatal CRH in the choice of behavioral strategy in stress.     

Thermally Enhanced Radiosensitivity of Cultured Chinese Hamster Cells

X-IRRADIATION of mammalian cells in culture yields a survival curve of the threshold type (for review see ref. 1). It isjnter-esting to ask how one can enhance the radiation response by small changes of the physical environment of the cells, as can be done chemically, for example, by incorporation of 5-bromo-deoxyuridine into DNA^1,2. Elevation of the temperature is a likely prospect for enhancement of radiosensitivity for the following reasons. It is known that proteins are heat labile and that temperature sensitive mutants of bacteria and phage can be obtained for many different enzymes³ which are operative at 37° C but not at 42° or 43°C. For example⁴, DNA polymerase is reversibly temperature sensitive; it is rendered inoperative above 42°C, but will be functional again when the temperature is lowered. It is not unreasonable to expect that temperature sensitive mutations for many enzymes occur frequently and that the use of temperatures somewhat higher than the normal range at which the cells grow might disclose sensitivities for specific enzymes in normal cells of higher organisms.