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 (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 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.

Mushroom Tyrosinase (MT) is a copper-containing enzyme, which is widely distributed in microorganisms, animals and plants. It is also a key enzyme in melanin biosynthesis, which plays a crucial role in determining the color of mammalian skin and hair. Nowadays melanoma is the one of the most terrified and lethal cancers. In this work, the modification of tyrosinase by Woodward’s reagent k has been done and its thermodynamic stability was investigated. For the study of stability, thermodynamic parameters obtained from thermal and chemical denaturation of the native and modified enzyme. Tm values in thermal denaturation showed thermal instability for modified enzyme. Tm values for the native and modified enzyme with different concentrations of the modifier (0.5, 1, 5 and 10 mM) were determined 61.2, 60.1, 58.3, 53.9 and 45.5 (0C) respectively. In chemical denaturation 8 M Guanidium Hydrochloride was used. The Cm (half of modifier’s concentration) and DGH2O (free energy) values for the native and modified enzyme were obtained. The values of ΔGH2O for the native and modified enzymes were 17.22, 16.75, 15.0, 13.7 and 11.5 KJ/mol and the values of Cm are 8.0, 7.5, 6.7, 10.0 and 8.0 (M) respectively. Thus, decreasing in values of DGH2O for the modified enzyme in comparison with its native form indicate the protein instability.

Diminishing protein aggregation by chaperone is very important factor in medicine and industry. In this paper, it is induced the chaperone ability for; b-casein upon modification of its acidic residues by Woodward reagent K (WRK) and examined on lysozyme as a target protein at pH 7.2 and outlined the mechanism for chaperone ability of modified system by UV-Vis and fluorescence spectroscopy and theoretical calculation methods.

Introduction Crown ethers are heteroaromatic compounds that act as host compounds in Host-Guest chemistry, and can form complexes with organic or inorganic cations or anions. Among the crown ethers, 18- Crown-6 has the potential to form stable complexes with cations such as K+, and NO+. These reagents have nanotube-like structures, their X-ray are presented in the following. Their preparation methods are given.

(A) Aromatic nitrations by tetranitromethane are revealed to be photo chemically offered and are supposed to progress via trinitromethyl nitrite [8].