9TH INTERNATIONAL/6TH EUROPEAN JOINT SYMPOSIUM ON PURINE AND PYRIMIDINE METABOLISM IN MAN

120 URATE TRANSPORT IN NEPHRONS OF GOUTY PATIENTS. Nakamura T, Tanaka T, Takagi K, Yoshio N, Inai K, Urasaki Y, Fukushima T, Tsutani H, Ueda T. Department of Medicine, Fukui Medical School, Fukui 910-11, Japan

According to the four component theory, urate transport in nephrons consists of 4 steps, glomerular filtration (GF), presecre- tory reabsorption, secretion and postsecretary reabsorption. We have been investigating quantitatively the relationship among the steps of urate transport and urinary urate excretion (Uua) using the formula

Uua = {Ccr- (1 - R1) + Cs} • Sua • (1 - R2)

where Sua: serum urate level, Ccr: creatinine clearance repre- senting the GF rate, RI: presecretory reabsorption rate, Cs: secretion rate, R2: postsecretory reabsorption rate. In 10 gouty patients with underexcretion and in 12 normal controls, Sua and Uua were determined before and after administration of various doses of pyrazinamides or benzbromarones. Using this formulas R1, Cs, R2 were calculated as 1.004, 39.0, 0.889 for gouty patients and 0.996, 63.4, 0.885 for normal controls, respectively. Inspite of a marked decrease in Cs, amounts of urate secretion (Cs × Sua) were only slightly reduced by the reduction in high Sua. In summary, Cs in the nephrons of gouty patients was signifi- cantly lower than that of normal controls, but R1 and R2 were almost equal in the two groups. The decrease in Cs was suspected of being the main cause of urate underexcretion in gouty patients.

121 THE ROLE OF XANTHINE OXIDASE IN REPER- FUSION INJURY AND THE MECHANISM OF IN- ACTIVATION OF XANTHINE OXIDASE BY NI- TRIC OXIDE Takeshi Nishino, K. Okamoto, N. Nagahara, Tomoko Nishino*, Y. Ichimori# and H. Nakazawa# Department of Biochemistry and Molecular Biology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113, Department of Biochemistry, Yokohama City University School of Med- icine, Yokohama 236, #Department of Physiology, School of Medicine, Tokai University, Isehara, Kanagawa 259-11, Japan

Objectives Xanthine oxidase and xanthine dehydrogenase are complex metaUoflavoprotein that represent alternate forms of the same gene product. Although the enzyme exists in the cell mostly as a dehydrogenase form, the enzyme can be converted to an oxidase form either by proteolysis or sulfhydryl oxidation of the protein molecule. This conversion was hypothetically proposed to be responsible for post ischemic reperfusion injury, but not significant conversion was observed during ischemic conditions in our experiments. However, the system can potentially produce significant amount of superoxide anion without conversion from the dehydrogenase to the oxidase due to accumulation of NADH and hypoxanthine. Allopurinol only partly inhibit the formation of super oxide. It was also found that xanthine oxidase was inactivated by nitric oxide in the presence of reducing substrate, forming the desulfo-form enzyme which naturally exists in the cell. This paper presents recent advances of our understanding of biochemistry and molecular biology of these systems including a model for the overall morphology of xanthine oxidizing enzymes and also represent the mechanism of inactivation of xanthine oxidase by nitric oxide and discuss about the role of the enzyme in post ischemia reperfusion injury.

122 ADENYLOSUCCINATE LYASE OF H U M A N BLOOD'S CELLS R. Pagani, R. Guerranti, G. Caldarelli, L. Brogi, G. Land- riscina, E. Marinello Insti tute of Biochemistry and Enzy- mology, University of Siena

Objectives An increased adenylosuccinate lyase activity is re- ported in some tumors. To verify if this occurs also in chronic lymphocytic leukemia, first we demonstrated the activity in all human blood's cells of healthy subjects. Design and Method After separation of all the cells, we removed the platelet contamination of the lymphocytes by immunochemi- cal procedure. Enzyme activity was measured by spectrophoto- metric assay. Results All the cells, including platelets and erithrocytes, show ASL activity, which has different values when referred either to 106 cells or to mg of protein. Conclusions The increased activity in the tumours can be due also only to the presence of a single isoform. Therefore, the study of the activity of the enzyme is not satisfactory, and we are devel- oping an enzymatic and immunochemical detection of isoenzymes after electrophoresis separation in order to demonstrate the presence of isoforms in the cells of leukemic patients.

123 A SYNDROME OF SEIZURES AND PERVASIVE DEVELOPMENTAL DELAY ASSOCIATED WITH EXCESSIVE CELLULAR NUCLEOTIDASE ACTIV- ITY Theodore Page,* John Fontenessi,t Alice Yu,t and William Nyhant, Departments of Neurosciences* and Pediatricst University of California, San Diego La Jolla, CA 92092 USA

Objectives Earlier we reported a syndrome characterized by frequent infections, seizures, ataxia, severe language delay, and unusual solitary, hyperactive behavior, associated with increased cellular nucleotidase activity. Our objective was to identify addi- tional patients with this syndrome and further study the bio- chemical abnormality. Design and Methods Fibroblast cultures were obtained from subjects who fit the phenotype. Nucleotidase activity and other biochemical tests were performed by the previously described methods. Results Three new patients were identified. In each case, nucle- otidase activity with both purine and pyrimidine substrates was increased 5- to 20-fold when compared to age-matched control cells. De novo purine synthesis was slightly decreased. No purine or pyrimidine enzyme deficiencies were found. Treatment with oral uridine was found to decrease seizures, ataxia, and infec- tions, improve language ability, and normalize behavior. Conclusion A number of patients with this syndrome exist, and in every case thusfar, it is associated with excessive nucleotidase activity.

124 D E NOVO PURINE SYNTHESIS IS INCREASED IN THE FIBROBLASTS OF PURINE AUTISM PA- TIENTS Theodore Page* and Mary Colemant, *University of Cali- fornia, San Diego La Jolla, CA 92093 USA tGeorgetown University School of Medicine Washington, DC 20008 USA

Objectives Previous studies have shown that approximately 25% of patients with classic autism excrete >14 mg/kg/day of uric acid. This study was undertaken to determine whether excessive purine synthesis could be demonstrated in the cells of these

272 CLINICAL BIOCHEMISTRY, VOLUME 30, APRIL 1997