Control of the regulatory enzyme threonine deaminase from Escherichia coli is achieved by isoleucine inhibition and valine activation. The mechanism by which these heterotropic effectors regulate the enzyme was investigated by measuring the binding of isoleucine and valine by spectroscopic, kinetic, calorimetric and equilibrium dialysis techniques. The addition of isoleucine or valine to threon...

organic acids exuded by plant roots increase solubility of soil micronutrient complexes. this study was carried out to evaluate adsorption isotherms of 4 acidic and 4 calcareous soils at presence of organic acids (citric, malic and oxalic acids). iron sorption and desorption isotherms are defined in to two systems including; system 1; soil-water-metal, system 2; soil-water-organic acid-metal). ...

abstract phosphorus (p) sorption in soils is a key process governing the availability of p to crops. p sorption characteristics and their relationship to soil properties were determined in twenty-one paired surface soil samples (21 cultivated and 21 adjacent virgin soils) belonging to five soil types: typic calcixerepts, typic haploxerepts, typic endoaquepts, vertic endoaquepts, and vertic calc...