Efficient factors in protein modification: ADenosine deaminase esterification by woodward reagent K

Chemical modification of Adenosine Deaminase (ADA) with N-ethyl-5-phenyl isoxazoliom-3-sulfonate (Woodward’s reagent K) (WR-K) was studied using experimental and theoretical techniques. Reaction concentration ranges were 0.8–6 mM WR-K at pH 7.8 and 27 °C. It was observed that the maximum number of moles of esterified residues per mol of enzyme ( $ \bar v $ ) in this concentration ranges is 4. However, esterification of ADA does not affect the activity of ADA, suggesting that the active site residues are not esterified. Similar results were obtained when the active site was blocked with 0.1 mM erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), followed by esterification, as measured by enol ester formation using absorbance at 340 nm. A theoretical approach was employed to study the modification process using molecular dynamic simulation, MM and QM/MM minimization. A full ASA empirical model and B3LYP method were used to evaluate the relative stability of some species which may arise from the reaction of ADA with WR-K. Theoretical results have shown that five residues (Glu 244, Glu 121, Glu 337, Asp 127, Asp 338) can be possible cases for modification in reaction 1:1 between ADA and WR-K at $ \bar v = 1 $ . Glu 121 was possible initially modified in this process. Besides, it is specified that atomic accessible surface area cannot be an appropriate criterion in determination of primary sites which are modified by WR-K. Ultimately, it is clarified that among effective factors in modification of enzyme surface such as atomic accessible surface, stability of modified segment and local residues changes of ADA, latter factor plays a basic role in this process from kinetics and thermodynamics point of view.     

On the use of homotopy analysis method for solving unsteady MHD flow of Maxwellian fluids above impulsively stretching sheets

In the present work, unsteady MHD flow of a Maxwellian fluid above an impulsively stretched sheet is studied under the assumption that boundary layer approximation is applicable. The objective is to find an analytical solution which can be used to check the performance of computational codes in cases where such an analytical solution does not exist. A convenient similarity transformation has been found to reduce the equations into a single highly nonlinear PDE. Homotopy analysis method (HAM) will be used to find an explicit analytical solution for the PDE so obtained. The effects of magnetic parameter, elasticity number, and the time elapsed are studied on the flow characteristics.