A mutant hypoxanthine-phosphoribosyltransferase (EC 2.4.2.8.) from a patient with gout is examined. The activity of the erythrocyte enzyme is about 5% of normal in this case. Immunoprecipitation studies using antiserum against highly purified human hypoxanthine-phosphoribosyltransferase reveal that the patient's erythrocytes contain a normal amount of cross-reacting material. The mutant enzyme has an altered net charge as shown by preparative isoelectric focusing (pI values of 5.75 and 4.55). The influence of chemical modification on enzymic activity was studied using a number of different reagents directed against sulfhydryl-, amino-, and guanidino-groups. Compared with normal hypoxanthine-phosphoribosyltransferase the mutant enzyme shows a generally lowered susceptibility to active site-directed inhibition. It is concluded that the patient's enzyme is the product of a structural mutation.

A patient with clearly developed features of the full Lesch-Nyhan syndrome and complete lack of activity of hypoxynthine-phosphoribosyltransferase is described. The clinical picture was characterized by absence of spasticity, good control of autoaggression by behavior therapy, and no signs of renal insufficiency. After death, which was caused by a viral infection, pathological examination and a search for material immunologically cross-reacting with hypoxanthine-phosphoribosyltransferase were possible. In spite of increased serum urate levels and raised urinary uric acid excretion there were no signs of urate deposits or damage in the internal organs, including the kidneys. Crossreactive material was found in the liver, kidneys and spleen, a relatively rare finding in the full Lesch-Nyhan-syndrome. The absence of any specific pathological changes in the brain of this patient is in agreement with earlier reports.

The activity of ecto-nucleotidases has been determined on intact cells from Burkitt lymphoma (BL) and lymphoblastoid cell lines established in vitro (LCLs). BL cells never express ecto-5'-nucleotidase (5'-N) and exhibit only low levels of ecto-ATPase activity, whereas LCL-cells usually express both enzymes to varying degrees. There is a certain correlation (r = 0.75) between 5'-N and ecto-ATPase. When cAMP formation in response to agonists of the A2-type (stimulating) adenosine receptor is measured in the same cell lines there is no correlation with the expression of ecto-nucleotidases. Within pairs of BL and LCL cell lines derived from the same donor, an inverse relationship between ecto-nucleotidases and the response to the adenosine receptor agonist N-ethyl-carboxamido-adenosine (NECA) is observed. BL cells show a good response to NECA, whereas this is low or absent in LCL cells. Treatment of cells which exhibit both 5'-N and the adenosine receptor with specific polyclonal or monoclonal antibodies against the enzyme does not impair the function of the receptor. Antisera against peptides of the membrane antigen BNLF I-MA, coded by the EBV-genome, do not co-precipitate 5'-N out of detergent extracts of LCL-cells. In both cases 5'-N cannot be closely associated with other membrane components. The differences between BL and LCL cells in ectonucleotidases and the adenosine receptor appear to be fairly stable phenotypical markers, independent of other parameters and suitable for use in distinguishing these cells in all populations.

Inactivation of hypoxanthine phosoxidized purine nucleosides do not influence phoribosyltransferase caused by periodate-oxiribosephosphate pyrophosphokinase, 5'-nucleotidized GMP is irreversible, even under the condidase, purine-nucleoside phosphorylase and guations of polyacrylamide gel electrophoresis and nylate kinase. A variety of other purine nucleoduring affinity chromatography on GMP-Sephasides and nucleotides, tested in their periodaterose. Partial binding of the inhibitor to the enoxidized form, do not lead to a compound comzyme protein can be demonstrated on dodecylparable or superior to oxidized GMP in its effect sulfate gel electrophoresis: The substrate, phoson hypoxanthine phosphoribosyltransferase. In phoribosyl diphosphate in the presence of Mg 2 ®, an erythrocyte system it is clearly demonstrated and the product GMP protect the enzyme against that oxidized GMP cannot act across an intact inactivation. Periodate-oxidized GMP, AMP and cell membrane.

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