Uric acid isotope studies

Table 1. Results of uric acid turnover studies by isotope dilution methods. I studies during purine-free, iso-energetic liquid formula diet II studies during purine supplementation. Subject 1-3 were studied using 15 N-uric acid. Subject 4 and 5 were studied after injection of 13 C-uric acid.

The Mechanism of the Oxydation of Uric Acid Studied with Isotopic... 

It is curious that there have been more fundamental developments in 1,3,5-triazine synthesis by this method than in any of the other sections, yet it is the oldest of all the synthetic routes. Cyanuric acid was originally prepared by the pyrolysis of uric acid (7) (see Section 2.20.1.2). The mechanism was proposed by Brandenberger and coworkers on the basis of isotopic labelling studies, and was reviewed by Modest (B-61MI22000, p. 706). The rearrangement of pyrimidines to 1,3,5-triazines is the most important advance in this area. 

The isolation of allantoin (7), after lead peroxide oxidation of uric acid was followed by the recognition of other oxidation products, the main product of which are oxonic acid (8), allantoxaidine (9) and oxaluric acid (HjNOCHNCOCOjH). Their structures have been clarified by comprehensive studies using isotopically labeled compounds. ... 

Nyhan later described another patient who was a hyperexcretor and displayed the associated clinical symptoms. This child synthesized uric acid from labeled glycine 200 times as rapidly as did normal controls (N5). Another aspect of Nyhan s studies was the rapid decrease of labeled uric acid from patients given glycine- C. The fact that, a week after administration of the isotope, the radioactivity of uric acid in the control and the patients under study approached approximately the same value would seem to indicate that the initial large amount of labeled uric acid was formed by the synthesis of purine nucleotides, which were rapidly broken down and did not involve an increased turnover of nucleic acid per se. It reflects a labile nucleotide pool, not a highly labeled one. 

Bl4. Benedict, J. D., Forsham, P. H., and Stetten, D., Jr., The metabolism of uric acid in the normal and gouty human studied with the aid of isotopic uric acid. J. Biol. Chem. 181, 183-193 (1949). 

Bishop, C., Gamer, W., and Talbott, J.H. Pool size, turnover rate, and rapidity of equilibration of injected isotopic uric acid in normal and pathological subjects. J. Clin. Invest., 30 879,1951. Yu, T.-F., Weissmann, B., Shamey, L., Kupfer, S., and Gutman, A.B. On the biosynthesis of uric acid from glycine- NS in primary and secondary polycythemia. Am. J. Med., 21 901, 1956. Laster, L., and Muller, A.F. Uric acid production in a case of myeloid metaplasia associated with gouty arthritis, studied with N -labeled glycine. Am. J. Med., 15 857,1953. 

Early studies with labeled compoimds were conducted simply to determine if adminbtered isotopes could be found in urinary uric acid or in the purines of tissue nucleic acids. More information was to be gained, however, by localizing the label in specific positions in the purine ring, and methods were therefore developed by which the uric acid molecule could be chemically degraded and each ring atom separately isolated. 

His diet was essentially the same during the three studies. %-glycine C60 atan % excess), 100 mg/kg body weight was given with 250 ml milk. Thereafter, urine was collected daily for one we, using toluene as preservative. Uric acid was determined using the uricase method. Uric acid was isolated and crystallized. Isotope enrichment was analyzed by standard mass spectroneter techniques as previously described CD. ... 

ISOTOPE STUDIES OF URIC ACID METABOLISM DURING DIETARY PURINE ADMINISTRATION... 

Uric acid is excreted by the kidneys and intestinal tract, while other routes are negligible. By addition of purines to a purine-free or low purine diet changes in uric acid turnover and excretion occur, which cannot be investigated by metabolic balance methods as that part of the uric acid turnover secreted into the gut is completely destroyed by the intestinal flora (Sorensen, i960). We therefore studied uric acid pool size and turnover in normal subjects both during a purine-free diet and during purine supplementation by stable isotope methods. 

Howell, R. R., M. Speas, and J. B. Wyngaarden. 1961. A quantitative study of recycling of isotope from glycine-l-C 0t Nl5 into various subunits of the uric acid molecule in a normal subject. J. Clin. Invest. 40 2076. 

The catheter was then cut near its insertion into the skin and from three to ten serial samples of subcutaneous fluid were collected in attached capillary tubes. Aliquots of each sample were assayed for uric acid and for both isotopes. The results of one such study are shown in the next slide. The concentrations of the labelled molecules, and of unlabelled urate are expressed as a percentage of their concentration in the injectate and are plotted against time. 

There have been many appllcaticms of isotope dilution analysis in biochemistry and medicine. Studies include measurement of erythrocyte volume with Cr labeled erythrocytes measurement of plasma volume with I labeled serum albumin measurement of body water with 1 labeled fexio-antipyrene or tritiated water measurement of extracellular space with Bn measiunement of total body pools of cholesterol, urea and uric acid with and sodium and potassium pool measurement with Na and K respectively. 

Studies with labeled lactic acid demonstrated that the carboxyl and a-carbons of lactate were converted into carbons 4 and 5 of uric acid, respectively. Since CO2 is the specific precursor of Ce, it was thought that lactic acid was converted into a 2-carbon compound prior to its utilization for uric acid formation. In view of the demonstration by Shemin of the conversion of serine to glycine, it was postulated that lactate was converted to serine which was then degraded to glycine, the latter being the more immediate purine precursor. This was confirmed by experimental evidence when high isotope concentrations were found in C4 after administration of carboxyl-labeled glycine. 

AIC has been synthesized with C in position 4 of the imidazole ring and its metabolism studied in animal tissues. It was converted into uric acid by the pigeon, while very little of the label appeared in the respiratory COs. A significant conversion of isotopic AIC into nucleic acid purines and nucleotide purines has been shown when this compound was injected into rats, and similarly into nucleic acid purines in mice. In addition, Williams has shown that it was appreciably converted into the purine compounds of resting and growing yeast. Thus, there is ample evidence that AIC may be converted into a complete purine ring in vivo. 

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