African Journal of Biochemistry Research Vol.2 (11), pp.219-224 November, 2008 Available online at http://www.academicjournals.org/AJBR ISSN 1996-0778 © 2007 Academic Journals Full Length Research Paper Study of sensitivity and ability of adenosine deaminase in response to pre-unfolding and especially pathological temperatures via changing the enzyme structure and activity Mostafa Rezaei-Tavirani 1,2 *, Saeed Hesami-Takallu 3 , Seyed Hassan Moghaddamnia 1 , Shiva Kalantari 4 , Bijan Ranjbar 5 , Seyedeh Zahra Moosavi-Nejad 6 , Sayed-Amir Marashi 7 , Mohammad Rahmati Roodsari 2 and Farhad Malekzad 2 1 Clinical Proteomics Research Center, Faculty of Paramedical Sciences, Shahid Beheshti University (M.C.), Tehran, Iran. 2 Skin Research Center, Shahid Beheshti University (M.C.), Tehran, Iran. 3 Science and Researches Branch, Islamic Azad University, Tehran, Iran. 4 Asre-Novin Institute of Research and Industrial Services, Unit 12, No. 38 (Malek Building), Tajrish Sq., Fana-Khosro Ave., Tehran, Iran. 5 Department of Biophysics, Faculty of Science, Tarbiat Modarres University, Tehran, Iran. 6 Department of Biology, Faculty of Science, Alzahra University, Tehran, Iran. 7 IMPRS-CBSC, Max Planck Institute for Molecular Genetics, Berlin, Germany. Accepted 26 th November,2008 Adenosine deaminase (ADA) is an important enzyme of the purine metabolic pathway, which catalyzes the conversion of adenosine and deoxyadenosine to their respective inosine derivatives plus ammonia, in a rapid and irreversible reaction. In this work, we studied the structural and kinetic properties of bovine ADA as a function of temperature in the range, 20 - 80°C by circular dichroism (CD) and UV- spectrophotometric techniques, as well as by measuring its activity in this temperature range. The results suggest that thermal unfolding of ADA occurs at temperatures above 60°C, while the enzyme undergoes detectable conformational changes during pre-unfolding heating. These changes affect the kinetics of reaction catalyzed by ADA. The relation between enzyme activity and structural changes is discussed. Key words: Adenosine deaminase (ADA), UV-Vis spectrophotometry, Conformational changes, Circular dichroism (CD), Kinetic study. INTRODUCTION Adenosine deaminase (ADA, EC 3.5.4.4) is a (/) 8 enzyme, which deaminates (deoxy)adenosine to (deoxy)inosine irreversibly (Cristalli et al., 2001). ADA is widely distributed in mammalian tissues and its role is critical in proliferation, maturation and function of lymphoid cells (Cristalli et al., 2001; Harutyunyan et al., 2005). Adenosine modulates the immune system and inhibits as inflammation via reduction of cytokine biosyn- *Corresponding author. E-mail: tavirani@sbmu.ac.ir, tavirany@yahoo.com. Tel and Fax: +98-21-22748836 thesis and neutrophil functions; therefore, ADA is involved in inflammation process. Its role in inflammation and malignancy has been studied experimentally and the results have been showed that ADA enzyme may play a role in inflammatory diseases of the pancreas (Ibis et al., 2007). Inhibition of adenosine deaminase results in a significant attenuation of intestinal inflammation (Antonioli et al., 2007). Aberrations in the expression and function of ADA have been implicated in several disease states such as severe combined immune deficiency (SCID), which is characterized by impaired B- and T-cell-based immunity resulting from an inherited deficiency in ADA (Cristalli et