Leaf litter ash alkalinity and neutralisation of soil acidity

Soil acidification is a major factor limiting the sustainability of agricultural production systems throughout the world. Liming may not always be economically possible and therefore alternative methods or complementary methods of amelioration are required. Leaf litter collected from several tree species was examined for ash alkalinity (as an estimate of organic anion content) and ability to ameliorate an acid soil. Ash alkalinity measured by titration of the ash and excess cation values obtained by calculation as the difference between cation and anion content were correlated. Values obtained by the latter method ranged from 247 cmol _c kg^-1 for Melia azedarach (white cedar) to 36 cmol _c kg^-1 for Eucalyptus globoidea (white stringybark). There was a significant linear correlation between ash alkalinity and the Ca concentration in the litter. When added to an acid soil (pH 4.04 measured in 0.01 M calcium chloride) and incubated for 8 weeks, leaf litter raised the pH. Species differed markedly with Melia azedarach having the greatest effect. The increase in pH was proportional to the quantity of ash alkalinity (organic anions) added, expressed as calcium carbonate equivalents. Aluminium levels on the exchange complex were lowered by treatment with leaf litter through direct precipitation of a solid phase and again Melia azedarach litter was most effective. There was also indirect evidence of organo-Al complexes affecting the concentration of monomeric Al in soil treated with litter from Liquidambar styraciflua (liquidambar), Quercus robur (English oak) and Pinus radiata (radiata pine).     

Effect of environmental acidity and alkalinity on the physiology of Tilapia mossambica during acclimation

The pattern of carbohydrate metabolism in the muscle of the freshwater fish, Tilapia mossambica (Peters) varied according to the pH of the environmental medium. On acclimation to a more acidic water, the white muscle showed an elevated glycogen content with suppressed glycolysis. In contrast, the muscle tissue showed an accelerated glycolytic pathway with the accumulation of metabotic acids on acclimation to a basic water. In an acidic medium phosphorylase activity was inhibited with an elevated LDH activity, while the reverse pattern was observed in an alkaline medium. The oxidative pathway was elevated in both. Acclimation to acidic and basic environmental waters leads to an adaptive compensatory mechanisms providing increased resistance capacity to the fish under pH stress.     

Modeling membrane proteins: The importance of cysteine amino-acids

Computational modeling of membrane proteins is critical to understand biochemical systems and to support chemical biology. In this work, we use a dataset of 448 non-redundant membrane protein chains to expose a “rule” that governs membrane protein structure: free cysteine thiols are not found accessible to oxidative compartments such as the extracellular space, but are rather involved in disulphide bridges. Taking as examples the 1018 three-dimensional models produced during the GPCR Dock, 2008, GPCR Dock, 2010, GPCR Dock, 2013 competitions and 390 models for a GPCR target in CASP13, we show that this rule was not accounted for by the modeling community. We thus highlight a new direction for model development that should lead to more accurate membrane protein models, especially in the loop domains.     

The inhibitory effect of polymeric carboxylic amino-acids and urine on calcium oxalate crystallization

A new method has been established to follow the inhibitory effect of some polymeric-dicarboxylic-amino-acids and other poly-anionic derivatives. The technique is based on using calcium specific electrode to measure continuously free calcium ion activity in solution to assess the formation of calcium oxalate precipitate.The retardation effect of Poly-L-glutamic and aspartic acids has been established in 5–100 ppm range and compared to other monomeric and polymeric compounds with inactivated functional groups. The retardation effect is in agreement with previous reports on inhibition effect on crystal growth rate of seed crystals, with the same retardants.The inhibitory effect was also determined with normal urine and compared to pathological urine.