A synthetic medium for ethanol production by recombinant xylose-fermenting Zymomonas mobilis was optimized using Plackett-Burman(PB) design and response surface methodology(RSM).The effects of 19 medium components were investigated by PB design.Eight of these components were determined to have significant effects on ethanol production.The statistical model was constructed via central composite design(CCD) using five selected variables,including xylose,trisodium citrate,choline chloride,pyridoxine,and thiamine.The validity of the developed model was verified.The ethanol concentration in the optimized medium was 6.7% higher than in the RM medium.The optimized medium was then simplified to give the final synthetic medium(S2),in which the ethanol concentration was 20.7% higher than in the RM medium.Xylose and trisodium citrate were the key medium components influencing ethanol production,while calcium pantothenate was the only growth factor required by recombinant Z.mobilis.Ethanol production and growth response were directly proportional to the logarithm of the concentration of trisodium citrate in the range of 0.1-1.6 g/L.
Due to inter-subunit communication, multisubunit enzymes usually hydrolyze ATP in a concerted fashion.However, so far the principle of this process remains poorly understood. In this study, from the viewpoint of statistical mechanics, a simple model is presented. In this model, we assume that the binding of ATP will change the potential of the corresponding enzyme subunit, and the degree of this change depends on the state of its adjacent subunits. The probability of enzyme in a given state satisfies the Boltzmann's distribution. Although it looks much simple, this model can fit the recent experimental data of chaperonin TRiC/CCT well. From this model, the dominant state of TRiC/CCT can be obtained. This study provide a new way to understand biophysical processe by statistical mechanics analysis.
