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Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human hypoxanthine/guanine phosphoribosyltransferase (EC 2.4.2.8) was purified from red blood cells by the following two methods. Method A includes (a) elimination of hemoglobin by DEAE-cellulose, (b) DEAE-Sephadex chromatography, (c) specific elution of the enzyme from CM-Sephadex by pyrophosphate and (d) Sephadex G-100 gel filtration. Method B includes (a) elimination of hemoglobin by DEAE-cellulose, (b) acid treatment at pH 4.5, (c) ammonium sulfate fractionation, (d) DEAE-Sephadex chromatography, (e) heat treatment at 85 degrees C and (f) Sephadex G-100 gel filtration. Homogeneous enzyme preparation was obtained by the two methods with 8000-9000-fold purification. The sedimentation coefficient (S20,w) was 5.5--5.6 S, and the molecular weight of the enzyme was estimated at about 85000 by the sedimentation equilibrium method. The subunit molecular weight of the untreated protein and S-carboxymethylmaleyl protein was estimated as 41000--45000 by the sedimentation equilibrium method in the presence of guanidine hydrochloride. However, the subunit size estimated by the sodium dodecylsulfate gel electrophoresis was only 26000. Amino acid composition of the enzyme was determined. Glucosamine, sialic acid and hexose were not detected in the enzyme.
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PMID:Purification and characterization of human hypoxanthine/guanine phosphoribosyltransferase. 88 Sep 43

Giardia lamblia, an aerotolerant anaerobe, respires in the presence of oxygen by a flavin, iron-sulfur protein-mediated electron transport system. Glucose appears to be the only sugar catabolized by the Embden-Meyerhof-Parnas and hexose monophosphate pathways, and energy is produced by substrate level phosphorylation. Substrates are incompletely oxidized to CO2, ethanol and acetate by nonsedimentable enzymes. The lack of incorporation of inosine, hypoxanthine, xanthine, formate or glycine into nucleotides indicates an absence of de novo purine synthesis. Only adenine, adenosine, guanine and guanosine are salvaged, and no interconversion of these purines was detected. Salvage of these purines and their nucleosides is accomplished by adenine phosphoribosyltransferase, adenosine hydrolase, guanosine phosphoribosyltransferase and guanine hydrolase. The absence of de novo pyrimidine synthesis was confirmed by the lack of incorporation of bicarbonate, orotate and aspartate into nucleotides, and by the lack of detectable levels of the enzymes of de novo pyrimidine synthesis. Salvage appears to be accomplished by the action of uracil phosphoribosyltransferase, uridine hydrolase, uridine phosphotransferase, cytidine deaminase, cytidine hydrolase, cytosine phosphoribosyltransferase and thymidine phosphotransferase. Nucleotides of uracil may be converted to nucleotides of cytosine by cytidine triphosphate synthetase, but thymidylate synthetase and dihydrofolate reductase activities were not detected. Uptake of pyrmidine nucleosides, and perhaps pyrimidines, appears to be accomplished by carrier-mediated transport, and the common site for uptake of uridine and cytidine is distinct from the site for thymidine. Thymine does not appear to be incorporated into nucleotide pools. Giardia trophozoites appear to rely on preformed lipids rather than synthesizing them de novo.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Biochemistry and metabolism of Giardia. 265 35