Temperature dependence of superoxide dismutase activity in plankton

The effect of temperature (from 1 to 37 °C) on in vitro effective superoxide dismutase (SOD) activity of several organisms was investigated and compared. Antarctic plankton, cultures of the alga Nannochloropsis sp., and the cyanobacterium Synechococcus strain WH 7803, and pure bovine erythrocyte SOD was studied. It was found that in all cases SOD activity increased with decreasing temperature within the temperature range assayed, in the Polar as well as the temperate plankton cells. This behavior of SOD is counterintuitive in terms of our experience when looking at enzyme activity or any other chemical reaction. We suggest a theoretical explanation for this apparently odd behavior. The advantage of such behavior is that the same amount of antioxidant will act better under low temperatures when reactive oxygen species (ROS) increase. Moreover, this protective process would act in vivo at a faster pace than the ex novo enzyme synthesis.     

Pressure effects on lipid-protein interactions in (Na+ + K+)-ATPase

The (Na⁺ + K⁺)-stimulated ATPase activity decreases with increasing pressure and a plot of the logarithm of the activity versus pressure shows a change in slope at a defined breakpoint pressure (P_b). The value of P_b increases linearly with increasing temperature. A $\text{d}\text{T}\text{d}\text{P}$ value of 27.7 ± 0.4 (S.D.) K/1000 atm is obtained. This is in very good agreement with the pressure shift for the melting transitions in phospholipids and aliphatic chains. This strongly indicates that an aliphatic chain melting process is involved in the breakpoint in the Arrhenius plot and pressure dependence of (Na⁺ + K⁺)-ATPase. The p-nitrophenyl phosphatase activity of this enzyme also decreases with pressure. In this case the plot of the logarithm of the activity versus pressure is linear without a break-point. The temperature dependence for (Na⁺ + K⁺)-ATPase was also studied in the presence of fluidizing drugs: desipramine and benzylalcohol. The presence of these drugs had no effect on the inflection point in the Arrhenius plot.     

PERSPECTIVE: THE THEORIES OF FISHER AND WRIGHT IN THE CONTEXT OF METAPOPULATIONS: WHEN NATURE DOES MANY SMALL EXPERIMENTS

We critically review the two major theories of adaptive evolution developed early in this century, Wright's shifting balance theory and Fisher's large population size theory, in light of novel findings from field observations, laboratory experiments, and theoretical research conducted over the past 15 years. Ecological studies of metapopulations have established that the processes of local extinction and colonization of demes are relatively common in natural populations of many species and theoretical population genetic models have shown that these ecological processes have genetic consequences within and among local demes. Within demes, random genetic drift converts nonadditive genetic variance into additive genetic variance, increasing, rather than limiting, the potential for adaptation to local environments. For this reason, the genetic differences that arise by drift among demes, can be augmented by local selection. The resulting adaptive differences in gene combinations potentially contribute to the genetic origin of new species. These and other recent findings were not discussed by either Wright or Fisher. For example, although Wright emphasized epistatic genetic variance, he did not discuss the conversion process. Similarly, Fisher did not discuss how the average additive effect of a gene varies among demes across a metapopulation whenever there is epistasis. We discuss the implications of such recent findings for the Wright-Fisher controversy and identify some critical open questions that require additional empirical and theoretical study.     

The relationship between iron status and lead absorption in rats

The absorption of lead from loops of small intestinein situ was investigated in rats in which iron absorption was increased by stimuli varying in type, intensity, or duration. Lead absorption was increased by a short period of severe iron restriction before any change in hematological indices became apparent. A period of hypoxia, which markedly increased iron absorption, did not influence absorption of lead. An extended period of moderate iron restriction resulted in a marked reduction in liver iron stores and increased iron absorption throughout the 17-wk experiment. Under these conditions lead absorption was initially also increased, but after 12 wk, when iron intake had become adequate to meet essential requirements, lead absorption was similar to that in iron-supplemented rats. These results are discussed in the light of evidence for a receptor-mediated absorption process for iron.     

Determination of optimal planning target volume margins in patients with gynecological cancer

PurposeTo define optimal planning target volume (PTV) margins for intensity modulated radiotherapy (IMRT) ± knee-heel support (KHS) in patients treated with adjuvant radiotherapy.MethodsComputed tomography (CT) scans ± KHS of 10 patients were taken before and at 3rd and 5th week of treatment, fused and compared with initial IMRT plans.ResultsA PTV margin of 15 mm in anteroposterior (AP) and superoinferior (SI) directions and 5 mm in lateral directions were found to be adequate without any difference between ± KHS except for the SI shifts in CTV-primary at the 3rd week. Five mm margin for iliac CTV was found to be inadequate in 10–20% of patients in SI directions however when 7 mm margin was given for iliac PTV, it was found to be adequate. For presacral CTV, it was found that the most striking shift of the target volume was in the direction of AP. KHS caused significantly less volume of rectum and bladder in the treated volume.ConclusionsPTV margin of 15 mm in SI and AP, and 5 mm in lateral directions for CTV-primary were found to be adequate. A minimum of 7 mm PTV margin should be given to iliac CTV. The remarkable shifting in presacral CTV was believed to be due to the unforeseen hip malposition of obese patients. The KHS seems not to provide additional beneficial effect in decreasing the shifts both in CTV-primary and lymphatic, however it may have a beneficial effect of decreasing the OAR volume in PTV margins.