The biological significance of purine salvage

Bone cells in culture: morphologic transformation by hormones

Hormones and purine nucleosides and nucleotides induced cultured bone cells to transform transiently from a spherical to a stellate shape. Cytochalasin B also induced the transformation. The change was blocked by colchicine and vinblastine, but not by lumicolchicine or cycloheximide. This morphologic transformation may provide a dynamic model of hormone action and bone cell modulation in vitro.

The metabolism of adenine derivatives in different parts of the brain of the rat, and their release from hypothalamic preparations on excitation

Five enzymes concerned with the metabolism of adenine derivatives were assayed in seven regions of the rat brain. A region which included the hypothalamus had the highest AMP deaminase and adenosine deaminase activities, while its 5'-nucleotidase activities were relatively low. The enzymes named and also the uptake of [14C]adenine by incubated tissue samples were more active with hypothalamic than with neocortical tissues. On superfusion with glucose-bicarbonate saline after assimilating [14C]adenine, the hypothalamic tissues released about 0.2 per cent of their 14C content per minute. This release was increased fourfold with electrical excitation but the presence of 0.25 muM tetrodotoxin prevented most of this increase. The compounds released during superfusion and electrical stimulation were preponderantly hypoxanthine, inosine, and adenosine, with only small amounts of adenine nucleotides. The output of all these compounds increased during the period of stimulation and also the proportion of adenine nucleotides increased when stimulation was carried out in the presence of tetrodotoxin. The output of the nucleotides and adenosine increased more promptly when stimulated than did that of the other compounds named. The results are discussed in terms of the metabolic roles of the enzymes concerned. and in relation to whether the enzymes are acting on intracellular or extracellular substrates.

Adenosine phosphyorylase activity as distinct from inosine-guanosine phosphorylase activity in Sarcoma 180 cells and rat liver

Adenosine phosphorylase (EC 2.4.2.-) activity present in Sarcoma 180 cells grown in culture and in rat liver, is shown to be distinct from inosine-guanosine phosphorylase by several criteria: (a) treatment of Sarcoma 180 cell extract with p-chloromercuribenzoate inhibited the two activities to a different extent, (b) adenine selectively protected the adenosine phosphorylase activity of Sarcoma 180 and rat liver extract against heat inactivation, while hypoxanthine selectively protected inosine-guanosine phosphorylase activity, (c) at nearly saturating substrate concentrations and using Sarcoma 180 extract, the rates of ribosylation of a mixture of adenine + hypoxanthine or adenine + guanine, but not of hypoxanthine + guanine, were found to be almost equal to the sum of their individual rates as measured separately, (d) inosine selectively inhibited the ribosylation of hypoxanthine and guanine catalysed by Sarcoma 180 and rat liver extract while 2-chloroadenosine selectively inhibited the ribosylation of adenine and N6-furfuryladenine, (e) pH vs. activity curves were similar with hypoxanthine or guanine as the substrate but they were markedly different from the curve with adenine as the substrate. The potential role of adenosine phosphorylase activity in vivo is discussed.

An improved method for the determination of 5-phosphoribosyl 1-pyrophosphate

A spectrophotometric method for the determination of 5-phosphoribosyl 1-pyrophosphate (PRPP) is presented which shows several advantages in comparison to the radiochemical techniques, such as a relatively simple, rapid and less expensive procedure. This technique has been used to evaluate PRPP content in erythrocytes, leukocytes and lymphocytes of normal subjects and individuals with partial hypoxanthine guanine phosphoribosyltransferase (EC 2.4.2.8) deficiency. The results obtained proved to be completely reliable in both groups of subjects examined, with values of PRPP similar to those observed by radiochemical techniques.

Evidence for purine biosynthesis in human leukocytes

Human leukocytes and lymphocytes have shown to be equipped with 5-phosphoribosyl-1-pyrophosphate amidotransrease, the enzyme which catalyzes the synthesis of the first intermediate of the purine pathway, thus providing evidence that these cells have the capacity for de novo purine biosynthesis.

Organ-specific effects of DNA methylation by alkylating agents in the inbred Swiss mouse

Young adult inbred Swiss mice given single or repeated equitoxic doses of N-methyl-N-nitrosourea (MNUA) or methyl methanesulphonate (MMS) develop thymomas and pulmonary adenomas only following MNUA in spite of nearly identical overall alkylation of DNA of tumour target tissues by both agents due mainly to the biologically ineffective product 7-methylguanine. The main difference in DNA alkylation was the production of O6-methylguinine, a known pre-mutagenic product, by MNUA in amounts 10 or more times as large as following MMS. This supports the possibility that somatic mutations are a part of the process of carcinogenesis.

Combined immunodeficiency disease associated with adenosine deaminase deficiency. Report on a workshop held in Albany, New York, October 1, 1973

Fifty-five children with CID and known ADA status were studies at a workshop held in Albany, New York. Erythrocyte ADA determinations were performed in 22 of the 55 patients, 13 of whom were ADA negative. The ADA defect appears to be transmitted as an autosomal recessive trait. Some patients with CID and ADA deficiency have characteristic radiologic abnormalities of the skeleton, which are not found in other illnesses. The thymus glands of all patients with CID and ADA deficiency who could be examined have evidence of thymic involution manifested by presence of Hassall's corpuscles and differentiated germinal epithelium; this is in contrast to "classic" thymus findings in CID with normal ADA. Adenosine deaminase probably plays an important, although as yet undefined, role in lymphocyte development and/or function. The deficiency of ADA in CID is the first enzyme defect observed in a deficiency disease of specific immunity.

Metabolism of xanthine and hypoxanthine in the tea plant (Thea sinensis L.)

1. The metabolism of xanthine and hypoxanthine in excised shoot tips of tea was studied with micromolar amounts of [2(-14)C]xanthine or [8(-14)C]hypoxanthine. Almost all of the radioactive compounds supplied were utilized by tea shoot tips by 30 h after their uptake. 2. The main products of [2(-14)C]xanthine and [8(-14)C]hypoxanthine metabolism in tea shoots were urea, allantoin and allantoic acid. There was also incorporation of the label into theobromine, caffeine and RNA purine nucleotides. 3. The results indicate that tea plants can catabolize purine bases by the same pathways as animals. It is also suggested that tea plants have the ability to snythesize purine nucleotides from glycine by the pathways of purine biosynthesis de novo and from hypoxanthine and xanthine by the pathway of purine salvage. 4. The results of incorporation of more radioactivity from [8(-14)C]hypoxanthine than from [2(-14)C]xanthine into RNA purine nucleotides and caffeine suggest that hypoxanthine is a more effective precursor of caffeine biosynthesis than xanthine. The formation of caffeine from hypoxanthine is a result of nucleotide synthesis via the pathway of purine salvage.

Biochemical and enzymic changes during erythrocyte differentiation. The significance of the final cell division

1. The haemoglobin content of developing erythroblasts was shown to increase rapidly when the cells completed the final cell division of erythroid development and passed from the dividing into the non-dividing cell compartment. 2. The activity of carbonic anhydrase was measured and shown to increase continually throughout erythroid differentiation. The activity increased most rapidly in the polychromatic stage. 3. Catalase activity did not increase significantly during erythroid differentiation until the reticulocyte stage. 4. The activity of four enzymes, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, adenosine deaminase and nucleoside phosphorylase, exhibited a similar pattern of change during erythroid differentiation. In the dividing cell compartment their activity was relatively high but exhibited a steep decline between the polychromatic stage and the orthochromatic stage, that is, as the cell completed its final cell division and moved from the dividing to the non-dividing compartment. After this the activity of these enzymes was stabilized at a relatively low value, and this activity persisted at such a value until the reticulocyte stage. 5. Lactate dehydrogenase activity also declined after the cell had crossed from the dividing into the non-dividing stage, but in this case the decline was less than in the case of the above four enzymes. 6. Adenylate kinase activity was relatively constant in the dividing cell compartment but exhibited a 60 percent increase when the cell passed from the dividing into the non-dividing compartment. 7. The cessation of cell division appears to coincide with a set of complex biochemical changes.

Utilization of the nucleic acids of Escherichia coli and rumen bacteria by sheep

1.Escherichia coliand mixed cultures of rumen bacteria were grown with [8-14C]adenine to label their nucleic acids specifically.

2. The labelled bacteria were injected into the rumen of sheep and the radioactivity incorporated into tissue nucleic acids and that excreted in the urine and faeces was determined.

3. The radioactivity was present in the cold trichloroacetic acid-soluble fraction and the RNA and DNA fractions of all tissues examined. Liver, kidney, spleen, and blood had the highest levels of radioactivity.

4. The radioactivity of the RNA was present only in adenosine monophosphate and guanosine monophosphate.

Clinical and biochemical studies on treatment of Lesch-Nyhan syndrome

The clinical findings in a previously unreported case of the Lesch-Nyhan syndrome are described. Though formal intellectual testing is very difficult because of the severe choreoathetosis and compulsive self mutilation, cognition appears to be less severely damaged than motor functions. It is most important to devise an active education programme for these children, and to control their self mutilation. Extracting all the teeth is strongly recommended from the latter point of view. Replacing the deficient enzyme by means of exchange blood transfusion was associated with only a transient and small decrease of the serum uric acid level; the urinary uric acid excretion was not significantly altered. The blood levels of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) had not decreased to about 10% of the mean normal range until 90 days after the transfusion. The patient's motor state was not improved by any of the following. (i) Exchange blood transfusion; (ii) oral adenine and allopurinol; (iii) tetrabenazine; (iv) thiopropazate; (v) chlorpromazine. His scores in the Reynell Development Language scale tests improved during the 14-month period of observation, but the present evidence does not justify attributing this to any of the attempted treatments. Some possible reasons for the apparent failure of transfusion to suppress purine synthesis or to improve the neurological disorder are discussed. The present clear evidence that HGPRT-containing cells remain in the circulation in sufficient numbers to keep the HGPRT activity above 10% of the normal value for at least 90 days, suggests that it would still be justifiable to investigate a similar treatment in the neonatal period.

Hypoxanthine-guanine phosphoribosyltransferase variant associated with accelerated purine synthesis

We have previously described a 14-yr-old boy with hyperuricemia, renal failure, and accelerated purine production resistant in vivo and in vitro to purine analogs. This patient demonstrated normal red cell hypoxanthine-guanine phosphoribosyltransferase (HPRT) heat stability, electrophoresis at high pH, and activity at standard substrate levels. In the present report an abnormal HPRT enzyme was demonstrated by enzyme kinetic study with phosphoribosylpyrophosphate (PRPP) as the variable substrate and inhibitory studies with sodium fluoride. Apparently normal HPRT activity in a patient with hyperuricemia and gout does not exclude a functionally significant HPRT mutation.

Partial purification and properties of the common inherited forms of adenosine deaminase from human erythrocytes

1. The partial purification of adenosine deaminase, types 1, 2 and 2-1, from human erythrocytes is described. 2. The isoenzyme components characteristic of the three forms of the enzyme were partially resolved by chromatography on DEAE-Sephadex. 3. Gel chromatography of the various forms of the enzyme gave estimates of the molecular weights in the range 30000-35000. 4. Electrophoresis in starch gels containing increasing percentages of starch did not reveal any differences in molecular weight between the genetic variants or their isoenzyme components. 5. Analytical isoelectric-focusing experiments in polyacrylamide gels gave the following pI values for the four isoenzyme components present in type 2-1 erythrocytes: 4.70, 4.83, 4.94 and 5.06. 6. All forms of the enzyme gave K(m) values for adenosine of about 30mum and K(i) values of about 8mum for the competitive inhibitor purine riboside. 7. Reaction rates of the type 1 and 2 enzymes were measured at different temperatures. Both enzymes gave values for the energy of activation for hydrolysis of adenosine of about 33.4kJ/mol (8kcal/mol). 8. Heat inactivation of all forms of the enzyme was markedly dependent on ionic strength, the rate of inactivation increasing with increasing ionic strength. The type 1 and type 2 forms of the enzyme differed significantly in their susceptibility to heat inactivation. From the variation of rates of inactivation with temperature, values were obtained for the energies of activation for the heat inactivation of both enzymes as follows: type 1 enzyme 275.5kJ/mol (65.9kcal/mol) and type 2 enzyme 241.6kJ/mol (57.8kcal/mol.).

8-Azaguanine resistance in mammalian cells. I. Hypoxanthine-guanine phosphoribosyltransferase

Chinese hamster cells were treated with ethyl methanesulfonate or N-methyl-N'-nitro-N-nitrosoguanidine, and mutants resistant to 8-azaguanine were selected and characterized. Hypoxanthine-guanine phosphoribosyltransferase activity of sixteen mutants is extremely negative, making them suitable for reversion to HGPRTase(+). Ten of the extremely negative mutants revert at a frequency higher than 10(-7) suggesting their point mutational character. The remaining mutants have demonstrable HGPRTase activity and are not useful for reversion analysis. Five of these mutants have < 2% HGPRTase and are presumably also HGPRTase point mutants. The remaining 14 mutants utilize exogenous hypoxanthine for nucleic acid synthesis poorly, and possess 20-150% of wild-type HGPRTase activity in in vitro. Their mechanism of 8-azaguanine resistance is not yet defined.

A possible role for 5-phosphoribosyl 1-pyrophosphate in the stimulation of uterine purine nucleotide synthesis in response to oestradiol-17

1. It has been reported that the rate of purine nucleotide synthesis de novo in the immature rat uterus is doubled at 6h after administration of oestradiol-17beta. The present work confirms an increased incorporation of glycine and adenine into uterine nucleotides between 2 and 6h after hormone treatment and investigates the mechanism of this response. 2. Activation of regulatory enzymes is unlikely to promote increased nucleotide synthesis: the activities of 5-phosphoribosyl 1-pyrophosphate amidotransferase (EC 2.4.2.14) and adenine phosphoribosyltransferase (EC 2.4.2.7) are the same in uterine extracts from control and oestrogen-treated rats. 3. Therefore it was proposed that oestradiol might promote an increased supply of a rate-limiting substrate. The low oestrogen-sensitive rate of AMP synthesis from adenine and endogenous 5-phosphoribosyl 1-pyrophosphate in the intact uterus compared with the high, oestrogen-insensitive rate in uterine extracts supplemented with 5-phosphoribosyl 1-pyrophosphate is evidence that the supply of 5-phosphoribosyl 1-pyrophosphate limits purine nucleotide formation and may increase after hormone treatment. This proposal is supported by the decrease in AMP synthesis in the whole tissue in the presence of guanine and 7-amino-3-(beta-d-ribofuranosyl)pyrazolo[3,4-d]pyrimidine (formycin). These compounds do not inhibit adenine uptake or adenine phosphoribosyltransferase activity, but they both decrease the availability of 5-phosphoribosyl 1-pyrophosphate, the former by promoting its utilization by hypoxanthine/guanine phosphoribosyltransferase (EC 2.4.2.8) and the latter by inhibiting its synthesis from ribose 5-phosphate and ATP by ribose 5-phosphate pyrophosphokinase (EC 2.7.6.1). 4. It is unlikely that the increased availability of 5-phosphoribosyl 1-pyrophosphate results from hormonal stimulation of ribose 5-phosphate formation. Methylene Blue and phenazine methosulphate both increase ribose 5-phosphate without altering the supply of 5-phosphoribosyl 1-pyrophosphate. 5. The activity of ribose 5-phosphate pyrophosphokinase is low in uterine extracts and increases rapidly in response to oestradiol. Therefore the hormonal activation of the routes of purine nucleotide synthesis both de novo and from preformed precursors may be due, at least in part, to an increased availability of the common rate-limiting substrate 5-phosphoribosyl 1-pyrophosphate, mediated by activation of ribose 5-phosphate pyrophosphokinase.