WITHDRAWN:Chimeric hypoxanthine guanine phosphoribosyltransferases: Effect of segment swapping on xanthine specificity and tetramer stability.

The paper entitled "Chimeric hypoxanthine guanine phosphoribosyltransferases: Effect of segment on xanthine specificity and tetramer stability", which was published online on 22 May 2006, was withdrawn at the author's request.

Plasmodium falciparum hypoxanthine guanine phosphoribosyltransferase. Stability studies on the product-activated enzyme.

Hypoxanthine guanine phosphoribosyltransferases (HGPRTs) catalyze the conversion of 6-oxopurine bases to their respective nucleotides, the phosphoribosyl group being derived from phosphoribosyl pyrophosphate. Recombinant Plasmodium falciparum HGPRT, on purification, has negligible activity, and previous reports have shown that high activities can be achieved upon incubation of recombinant enzyme with the substrates hypoxanthine and phosphoribosyl pyrophosphate [Keough DT, Ng AL, Winzor DJ, Emmerson BT & de Jersey J (1999) Mol Biochem Parasitol98, 29-41; Sujay Subbayya IN & Balaram H (2000) Biochem Biophys Res Commun279, 433-437]. In this report, we show that activation is effected by the product, Inosine monophosphate (IMP), and not by the substrates.