Thesis (doctoral)--Universität Hamburg, 1980.

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) catalyses the first step in purine salvage. A complete deficiency of the enzyme results in the devastating neurological symptoms of the Lesch-Nyhan syndrome. The Lesch-Nyhan syndrome is characterised by purine overproduction leading to, hyperuricemia and gout and a central nervous system disorder characterised by severe, spasticity, choreoathetosis, mental retardation and compulsive self-mutilatory behaviour, A partial deficiency of the enzyme results in purine overproduction, gout and occasionally, mild neurological symptoms. Patients are spared the compulsive self-mutilation of the Lesch-Nyhan syndrome. The major part of the thesis consists of the characterisation of the molecular defects in nine patients with the Lesch-Nyhan syndrome. The polymerase chain reaction was used to amplify reverse transcribed HPRT mRNA. The coding region of the amplified HPRT cDNA was either directly sequenced, or cloned and sequenced. All the mutations characterised were insertion or deletion events which resulted in premature termination of the predicted protein. Three patients were found to have a deletion of exon 7, two patients had single base insertions, while two patients appeared to have a complete deletion of the HPRT gene. An insertion in one patient was the result of a mutation within. intron 6 which created a new splice donor site. The new splice donor site in concert with a cryptic splice acceptor resulted in the creation of a new exon. A deletion of exons 2, 3 and 4 in another patient was found to lead to the alternative splicing of exon 5. These unusual splice junction mutations provided in viva support for the exon definition model of pre-mRNA splicing.

The patient (T.K.), was first diagnosed as having a partial hypoxanthine-guanine phosphoribosyltransferase deficiency in 1978 when he was 20 years old. At presentation, he complained of a colicky loin-pain which radiated into his groin, and that he had had dark urine for a month. He was shown to have haematuria and urate crystalluria, and had a serum urate of 0.8mmol/l (reference range 0.12-0.5mmol/l). The diagnosis was confirmed by demonstrating a haemolysate hypoxanthine-guanine phosphoribosyltransferase activity of 550μU/mg Hb (reference range 1680-2480μU/mg Hb). Studies to determine whether the low hypoxanthine-guanine phosphoribosyltransferase activity was caused by an altered Kₘ of the enzyme for one of its substrates, showed that there was substrate inhibition of the enzyme activity by hypoxanthine. This thesis examines the patient and the variant HPRT at three levels. Firstly, a detailed and comprehensive study of the kinetic properties of the variant enzyme was made. The novel feature of the kinetics is the presence of substrate inhibition by the purine bases, with a true Kᵢ value for hypoxanthine of 80± 20μM, and a normal value for the true Kₘ. The pattern of substrate inhibition is characteristic of that associated with the formation of a dead-end complex and double inhibition experiments indicate that the form of this complex is enzyme-hypoxanthine-PPi. These unusual kinetic properties provided an opportunity to study the order of substrate binding in a way not possible for the normal enzyme and showed an ordered sequential reaction mechanism. Some limited protein-structural studies were performed and showed an altered electrophoretic mobility for the variant enzyme in non-denaturing gels. Secondly, the purine metabolic pathways in cultured cells, derived from T.K., from a patient with the Lesch-Nyhan syndrome, and from normal individuals, were studied. The cells were labelled with precursors of the de novo or of the salvage pathways, usually in the presence of a reference label, and sometimes in the presence of inhibitors of the various steps in the purine metabolic pathways. Hypoxanthine salvage was about 10% of that of control cultures. The growth of cells in a variety of selective media was also studied. Thirdly, as physician in charge of T.K., I could monitor the progress of his hyperuricaemia and observe the effects of therapy throughout the duration of this project.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves 120-139).

Thesis (Ph.D). / Written for the Dept. of Human Genetics. Title from title page of PDF (viewed 2009/06/08). Includes bibliographical references.

Magister Scientiae - MSc / Malaria remains the most important parasitic disease worldwide. It is estimated that over 500 million infections and more that 2.7 million deaths arising from malaria occur each year. Most (90%) of the infections occur in Africa with the most affected groups being children of less than five years of age and women. this dire situation is exacerbated by the emrggence of drug resistant strains of Plasmodium falciparum. The work reported in this thesis focuses on improving the purification of PfHPRT by investigating the characteristics of anion exchange DE-52 chromatography (the first stage of purification), developing an HPLC gel filtration method for examining the quaternary structure of the protein and possible end stage purification, and initialcrystalization trials. a homology model of the open, unligaded PfHPRT is constructed using the atoomic structures of human, T.ccruz and STryphimurium HPRT as templates. / South Africa

Orientadores: Gonçalo Amarante Guimarães Pereira, Francisco Javier Medrano Martin / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-11T15:38:56Z (GMT). No. of bitstreams: 1 Dantas_DeysedeSouza_D.pdf: 4937353 bytes, checksum: 5c9b26f6ef8ed34e974ca6c8bb0708f2 (MD5) Previous issue date: 2008 / Resumo: Os genes que codificam para a 6-oxopurina fosforribosiltransferase (HPRT, EC2.4.2.8) dos organismos Pyrococcus horikoshii e Schistosoma mansoni foram clonados em vetores de expressão. As proteínas foram expressas e purificadas em larga escala no sistema de expressão de Escherichia coli. Estudos cinéticos mostraram que a enzima de P. horikoshii é capaz de usar hipoxantina, guanina e xantina. Os dois primeiros substratos apresentam uma eficiência catalítica semelhante. A xantina apresenta um valor menor (ao redor de 20 vezes mais baixo), mas a constante catalítica é comparável com a da hipoxantina. A proteína não foi capaz de se ligar a GMP-agarose, mas sim pode ligar o outro substrato da reação reversa, pirofosfato inorgânico, com baixa afinidade (Kd = 4,7 ± 0,1 mM). Os dados de espalhamento dinâmico de luz, gel filtração e espalhamento de raios X a baixo ângulo mostram que esta proteína é um homohexâmero em solução. Este hexâmero é compacto e resistente à ação limitada de enzimas proteolíticas. Estudos de estabilidade frente a agentes químicos mostraram que a proteína é bastante estável resistindo os efeitos da uréia sem desenovelar completamente com a maior concentração do agente (8,0 M). Os dados obtidos com cloreto de guanidina mostraram que a proteína possui, no mínimo, um estado intermediário de desnaturação, como mostram os diferentes perfis obtidos com as diferentes técnicas usadas nos estudos de desnaturação. Os dados preliminares obtidos com a HPRT de S. mansoni mostraram que, na presença da cauda de histidinas, a proteína está presente como um octâmero alongado. Mas, muito provavelmente ela deve ser um tetrâmero. A presença de caudas fusionadas nas proteínas recombinantes pode afetar a estrutura e função das proteínas / Abstract: The genes that code for the 6-oxopurine phosphoribosyltransferase (HPRT, EC2.4.2.8) from the organisms Pyrococcus horikoshii and Schistosoma mansoni were cloned in expression vectors. The proteins were expressed and purified in large scale in the de Escherichia coli expression system. Kinetic studies showed that the enzyme from P. horikoshii is able to use hypoxanthine, guanine and xanthine. The first two substrates show a similar catalytic efficiency. Xanthine show a lower value (around 20 times), but the catalytic constant is comparable to that of hypoxanthine. The protein was unable to bind to GMP-agarose, but was able to bind the other substrate of the reverse reaction, inorganic pyrophosphate, with low affinity (Kd = 4.7 ± 0.1 mM). Dynamic light scattering, gel filtration and small angle X-ray scattering data show that the protein is a homohexamer in solution. This hexamer is compact and resistant to the limited action of proteolytic enzymes. Stability studies with chemical agents showed that the protein is very stable being able to stand the effects of urea without unfolding completely at the highest agent concentration (8.0 M). Data obtained with guanidine hydrochloride showed that the protein presents, at least, one unfolding intermediate state, as can be seen with the different profiles obtained with different techniques used in the unfolding studies. Preliminary data obtained from HPRT from S. mansoni showed that in the presence of the histidine tag, is present as a long octamer. But, most likely it should be a tetramer. The presence of histidine tag fused to the recombinant proteins could affect the structure and function of proteins / Doutorado / Bioquimica / Doutor em Biologia Funcional e Molecular