A study on the activity and thermal stability of adenosine deaminase in the presence of spermine

Adenosine Deaminase is an aminohydrolase (EC 3.5.4.4) which participates in the purine metabolism where it degrades either adenosine or 2''-deoxyadenosine producing inosine or 2''-deoxyinosine, respectively. The enzyme contains a parallel alpha/beta -barrel motif with eight central beta strands and eight peripheral alpha helices. ADA is located both in the cytosol and on the cell membrane. Since spermine, a natural metabolite, exists in all cells and tissues and its effect on the cell proliferation and enzyme regulation have been reported, thermal inactivation of the ADA and spermine regulatory effect on the ADA activity have been investigated in this study. Percentage of ADA activity in the presence and absence of spermine (1000 µM) in Tris buffer 50 mM, pH 7.5 at physiologic and pathologic temperatures have been reported in the present study. Thermal inactivation curves for ADA in the absence and presence of spermine (1000 µM) in different temperatures ranging from 55 oC to 70 oC have been drawn. Our data showed that spermine activates the enzyme in the low concentrations of adenosine at 37 oC. However, it inhibits ADA activity at 42 oC in the same concentrations of substrate. It is concluded that spermine regulatory effect depends on combined influence of temperature and adenosine concentration. Furthermore, thermal stability of the enzyme also depends on temperature in presence of spermine. Binding site of spermine on the enzyme has been identified by docking analysis.