Thermodynamic Views of Inhibition, Activation and Denaturation of Adenosine Deaminase by Ring Opened Nucleosides and Denaturants

Abstract

Adenosine deaminase (ADA) is one of the important enzymes acting in the metabolism of nucleic acid components. Lack of ADA has been shown to be associated with inherited severe combined immunodeficiency (SCID) and acquired immunodeficiency syndrome (AIDS). A marked increase in ADA has also been implicated in a number of other clinical conditions including, hereditary haemolytic anaemia and leukemias. Therefore, the great importance of research on inhibition, activation of ADA is required.

Here, the inhibition and activation of ADA by derivatives of acyclic adenine nucleoside (Compounds I, II, C — IX) substituted at the ninth adenine position are studied and denaturation of ADA by sodium n — dodecyl sulphate (SDS) and dodecyl trimethylammonium bromide have been also considered kinetically and thermodynamically at phosphate buffer, pH 7.5 in various temperatures.

The type of inhibition was analysed thermodynamically, using melting point (T_m) as a sensitive point for conformational change. The activation and deactivation of ADA were also investigated by pK method to obtain the amino acids which are interacted with inhibitors and activator. The glutamic, aspartic acids and a little histidine was involved to C — IX for activation. The deactivation was occured by change on histidine only.

The denaturation of ADA was also studied to obtain more information on the structure of the enzyme. The interaction of SDS caused the folding, whereas DTAB caused the unfolding which is corresponded to activation and deactivation for ADA respectively. The folding of ADA by SDS induced the minimum solubility conformed at lower temperature which means the greater apolar interactions in the interior phase result in a lower value for T_H (temperature of minimum solubility), whereas it is inconsistent to unfolding state which is induced by ADA — DTAB complexes that is occured in a higher value for T_H.