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Ammonia Channeling in Plasmodium falciparum GMP Synthetase: Investigation by NMR Spectroscopy and Biochemical Assays

Bhat, Javaid Yousuf and Venkatachala, Roopa and Singh, Kavita and Gupta, Kallol and Sarma, Siddhartha P and Balaram, Hemalatha (2011) Ammonia Channeling in Plasmodium falciparum GMP Synthetase: Investigation by NMR Spectroscopy and Biochemical Assays. In: Biochemistry, 50 (16). pp. 3346-3356.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/bi1017057

Abstract

GMP synthetase, a class I amidotransferase, catalyzes the last step of the purine biosynthetic pathway, where ammonia from glutamine is incorporated into xanthosine 5'-monophospate to yield guanosine 5'-monnophosphate as the main product. Combined biochemical, structural, and computational studies of glutamine amidotransferases have revealed the existence of physically separate active sites connected by molecular tunnels that efficiently transfer ammonia from the glutaminase site to the synthetase site. Here, we have investigated aspects of ammonia channeling in P. falciparum GMP synthetase using biochemical assays in conjunction with N-15-edited proton NMR spectroscopy. Our results suggest that (1) ammonia released from glutamine is not equilibrated with the external medium (2) saturating concentrations of glutamine do not obliterate the incorporation of external ammonia into GMP, and (3) ammonia in the external medium can access the thioester intermediate when the ATPPase domain is bound to substrates. Further, mutation of Cys-102 to alanine confirmed its identity as the catalytic residue in the glutaminase domain, and ammonia-dependent assays on the mutant indicated glutamine to be a partial uncompetitive inhibitor of the enzyme.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 20 May 2011 07:05
Last Modified: 20 May 2011 07:05
URI: http://eprints.iisc.ernet.in/id/eprint/37690

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