Inactivation of Hypoxanthine Guanine Phosphoribosyltransferase by Guanosine Dialdehyde : An Active Site Directed Inhibitor

Abstract

Congenital deficiencies of the enzyme HGPRT are invariably associated with metabolic overproduction of purines, which manifest clinically as hyperuricaemia and gout (1). In cases of severe enzyme deficiency (Lesen Nyhan syndrome), these manifestations are accompanied by a bizarre neurological disorder (2). Production of the enzyme deficiency in laboratory animals would be a considerable experimental advantage in studying these disorders. This might be achieved by the use of active-site directed irreversible inhibitors of the enzyme (3). Although a wide range of substrate analogues have been synthesised, most have exhibited poor binding compared to the substrates. A more successful approach has been the modification of the enzyme reaction product GMP. GMP-dialdehyde, the periodate oxidation product of GMP, has been shown to be a specific irreversible inhibitor of HGPRT in cell extracts but was unable to penetrate the intact cell membrane (4, 5). The experiments reported here show that guanosine dialdehyde (GDA), the periodate oxidation product of guanosine, is also a relatively specific but less potent inhibitor of HGPRT and appears to be able to act intracellularly.