Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Plasmodium falciparum trophozoites were isolated by mechanical rupture of infected human erythrocytes followed by a series of differential centrifugation steps. After lysis with sonication, the 100 000 x g supernatant of parasites and uninfected host cells was used to determine the specific activities of a number of enzymes involved in purine and pyrimidine metabolism. P. falciparum possessed the purine salvage enzymes: adenosine deaminase, purine nucleoside phosphorylase, hypoxanthine-guanine phosphoribosyltransferase (PRTase), xanthine PRTase, adenine PRTase, adenosine kinase. The last two enzymes, however, were present at much lower activity levels. Hypoxanthine was converted (presumably via IMP) into adenine and guanine nucleotides only in the presence both of supernatant and membrane fractions of P. falciparum. Two enzymes involved in the de novo synthesis of pyrimidines, orotic acid PRTase, and orotidine 5'-phosphate decarboxylase, were present in parasite extracts as were the enzymes for pyrimidine nucleotide phosphorylation: UMP-CMP kinase, dTMP kinase, nucleoside diphosphate kinase. Xanthine oxidase, CTP synthetase, cytidine deaminase and several kinases for the salvage of pyrimidine nucleosides were not detected in the parasites. Both phosphoribosyl pyrophosphate synthetase and uracil PRTase were present but at low activity levels. Human erythrocytes displayed similar but not identical enzyme patterns. Enzyme specific activities, however, were generally much lower than those of the corresponding parasite enzymes.
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PMID:Enzymes of purine and pyrimidine metabolism from the human malaria parasite, Plasmodium falciparum. 628 90

Blockade of a metabolic pathway by interaction of a drug with a particular 'target enzyme' results in depletion of essential end-products of the pathway and accumulation of intermediates prior to the blockade. Metabolic resistance to a particular drug can arise if the substrate of the inhibited enzyme accumulates to levels sufficiently high to compete effectively with the inhibitor, leading to restoration of full activity of the metabolic pathway after a transitory delay. Such resistance has recently been demonstrated in vitro for the interaction of the tight-binding inhibitor N-phosphonacetyl-L-aspartate (PAcAsp) with the aspartate transcarbamoylase activity of the trifunctional protein which initiates pyrimidine biosynthesis in mammals [Christopherson, R. I. and Jones, M. E. (1980) J. Biol. Chem. 255, 11381-11395]. Carbamoyl phosphate, the product of the carbamoyl phosphate synthetase activity of this trifunctional protein, accumulates to a sufficiently high concentration that the inhibitory effect of PAcAsp is effectively abolished. We have developed a theoretical model for metabolic resistance which quantitatively accounts for these experimental data. This model has been used to simulate the interaction between the following potential or proven anti-cancer drugs and their target enzyme, under conditions similar to those which would occur in vivo: PAcAsp with aspartate transcarbamoylase; various OMP analogues [the 5'-monophosphates of 6-azauridine, pyrazofurin and 1-(beta-D-ribofuranosyl)-barbituric acid] with OMP decarboxylase; 5-fluorodeoxyUMP with thymidylate synthase; methotrexate with dihydrofolate reductase; and deoxycoformycin with adenosine deaminase.
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PMID:Metabolic resistance: the protection of enzymes against drugs which are tight-binding inhibitors by the accumulation of substrate. 687 66