INHIBITION BY 6-MERCAPTOPURINE OF PURINE PHOSPHORIBOSYLTRANSFERASES FROM EHRLICH ASCITES-TUMOUR CELLS THAT ARE RESISTANT TO THE DRUG

1. A strain of Ehrlich ascites-tumour cells that showed little inhibition of growth in the presence of 6-mercaptopurine accumulated less than 5% as much 6-thioinosine 5'-phosphate in vivo, in the presence of 6-mercaptopurine, as did the sensitive strain from which it was derived. 2. Specific activities of the phosphoribosyltransferases that convert adenine, guanine, hypoxanthine and 6-mercaptopurine into AMP, GMP, IMP and 6-thioinosine 5'-phosphate were similar in extracts of the resistant and the sensitive cells. 3. As found previously with sensitive cells, 6-mercaptopurine is a competitive inhibitor of guanine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase from the resistant cells and does not inhibit the adenine phosphoribosyltransferase from these cells. Michaelis constants and inhibitor constants of the purine phosphoribosyltransferases from resistant cells did not differ significantly from those measured with the corresponding enzymes from sensitive cells. 4. Resistance to 6-mercaptopurine in this case is probably not due to qualitative or quantitative changes in these transferases.

THE GENUS VEILLONELLA . II. NUTRITIONAL STUDIES

Rogosa, M. (National Institute of Dental Research, U.S. Public Health Service, Bethesda, Md.), and Ferial S. Bishop. The genus Veillonella. II. Nutritional studies. J. Bacteriol. 87:574-580. 1964.-A medium is described for the study of the vitamin, hypoxanthine, putrescine, or cadaverine requirements of 86 Veillonella isolates from man, rabbit, rat, and hamster. No organism required riboflavine or folic acid for growth. Niacin and calcium pantothenate were often stimulatory, but in nearly all cases were dispensable. Biotin and p-aminobenzoic acid were frequently stimulatory and sometimes indispensable for continued growth. V. parvula (antigenic group VI) required pyridoxal and thiamine and did not require putrescine or cadaverine. V. alcalescens (antigenic group IV) required pyridoxal, generally required thiamine, and also required putrescine or cadaverine. Of the isolates, 25 from the rat and 3 from the hamster (antigenic group II) generally behaved like V. parvula, except that a putrescine or cadaverine requirement was often observed. Spermine, spermidine, and agmatine could not replace putrescine or cadaverine. Although succinate is metabolized by resting cells, the organisms could not grow with succinate as an energy source.

REGULATION OF XANTHINE DEHYDROGENASE IN CHICK LIVER. EFFECT OF STARVATION AND OF ADMINISTRATION OF PURINES AND PURINE NUCLEOSIDES

1. The xanthine-dehydrogenase activity of chick liver, expressed per mg. of nitrogen, is increased during starvation. 2. Administration of inosine and possibly of adenine has a comparable effect on the xanthine dehydrogenase, and also induces an elevation of the total quantity of enzyme. Hypoxanthine, xanthine, guanine, xanthosine, guanosine and adenosine are ineffective. Cortisone is equally ineffective. 3. The administration of puromycin abolishes the effect of inosine and reduces that of starvation. It is concluded that inosine induces an increased synthesis of xanthine dehydrogenase, whereas during starvation the enzyme is spared with respect to other liver proteins. 4. The hypothesis is formulated that chick-liver xanthine dehydrogenase is an adaptive enzyme, its activity being regulated by inosine or by one of its metabolites.

INHIBITION OF PRUINE PHOSPHORIBOSYLTRANSFERASES OF EHRLICH ASCITES-TUMOUR CELLS BY 6-MERCAPTOPURINE

1. The formation of adenosine 5'-phosphate, guanosine 5'-phosphate and inosine 5'-phosphate from [8-(14)C]adenine, [8-(14)C]guanine and [8-(14)C]hypoxanthine respectively in the presence of 5-phosphoribosyl pyrophosphate and an extract from Ehrlich ascites-tumour cells was assayed by a method involving liquid-scintillation counting of the radioactive nucleotides on diethylaminoethylcellulose paper. The results obtained with guanine were confirmed by a spectrophotometric assay which was also used to assay the conversion of 6-mercaptopurine and 5-phosphoribosyl pyrophosphate into 6-thioinosine 5'-phosphate in the presence of 6-mercaptopurine phosphoribosyltransferase from these cells. 2. At pH 7.8 and 25 degrees the Michaelis constants for adenine, guanine and hypoxanthine were 0.9 mum, 2.9 mum and 11.0 mum in the assay with radioactive purines; the Michaelis constant for guanine in the spectrophotometric assay was 2.6 mum. At pH 7.9 the Michaelis constant for 6-mercaptopurine was 10.9 mum. 3. 25 mum-6-Mercaptopurine did not inhibit adenine phosphoribosyltransferase. 6-Mercaptopurine is a competitive inhibitor of guanine phosphoribosyltransferase (K(i) 4.7 mum) and hypoxanthine phosphoribosyltransferase (K(i) 8.3 mum). Hypoxanthine is a competitive inhibitor of guanine phosphoribosyltransferase (K(i) 3.4 mum). 4. Differences in kinetic parameters and in the distribution of phosphoribosyltransferase activities after electrophoresis in starch gel indicate that different enzymes are involved in the conversion of adenine, guanine and hypoxanthine into their nucleotides. 5. From the low values of K(i) for 6-mercaptopurine, and from published evidence that ascites-tumour cells require supplies of purines from the host tissues, it is likely that inhibition of hypoxanthine and guanine phosphoribosyltransferases by free 6-mercaptopurine is involved in the biological activity of this drug.

URIC ACID TRANSPORT SYSTEM: APPARENT ABSENCE IN ERYTHROCYTES OF THE DALMATIAN COACH HOUND

The Dalmatian coach hound appears to lack a mediated transport system for uric acid, which can be demonstrated in the erythrocytes of other dogs by hypoxanthine inhibition of uric acid uptake. This transport deficiency may be a manifestation of a genetic defect which has different metabolic consequences in the liver, in the kidney, and in other tissues, depending on the direction of their differentiation

DEAMINATION OF ADENINE AND RELATED COMPOUNDS AND FORMATION OF DEOXYADENOSINE AND DEOXYINOSINE BY LINGCOD MUSCLE ENZYMES

Adenylic acid deaminase was destroyed by heating crude extracts of lingcod muscle to 58 °C, while deamination of adenosine and deoxyadenosine was unaffected. Deoxyadenosine was deaminated about 2300 times as fast as adenine by the enzyme extract. The specific activity of the purine nucleoside phosphorylase with adenine and deoxyribose-1-phosphate as substrates was similar to that of the deoxyadenosine deaminase of the enzyme preparations. It can thus be stated with certainty that adenine is a substrate for the nucleoside phosphorylase, that deoxyadenosine thus formed is promptly deaminated to deoxyinosine, and that deamination of adenine to hypoxanthine plays a negligible role in formation of deoxyinosine. The presence of small amounts of deoxyadenosine in the above reaction was verified by radioactive adenine and isolation of deoxyadenosine of constant specific activity by addition of deoxyadenosine carrier.

URINARY EXCRETION OF SOME PURINE BASES IN NORMAL AND SCHIZOPHRENIC SUBJECTS

Kishimoto (1958) reported quantitative and qualitative peculiarities in the absorption spectra of body fluids in schizophrenia, and considered that there were abnormalities in the oxidation of adenine through hypoxanthine and xanthine to uric acid.