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At least 415 records · Page 23Linked to original sources
PubMed1975

In vitro evaluation of methotrexate and azathioprine for antipsoriatic activity.

The effects of methotrexate and azathioprine, two drugs used in antipsoriatic therapy, on oxygen consumption of surviving human skin and on enzymatic activities of human skin homogenates were investigated. In concentrations of 1 mM/1, both substances provoked a significant decrease in oxygen consumption of human skin; in this respect, there was practically no difference between methotrexate and azathioprine. In the enzyme assays, however, azathioprine was, by far, less effective than methotrexate. After an incubation of 120 min azathioprine (1mM/1) inhibited lactate and glucose-6-phosphate dehydrogenase activities by about 10 per cent only, whereas the corresponding values with methotrexate amounted to 80 and 70 per cent, respectively. Methotrexate revealed an immediate inhibitory effect on pure glucose-6-phosphate dehydrogenase whereas azathioprine produced no changes in this mode. Furthermore, only methotrexate inhibited "acid" phosphatase activity of human skin homogenates.--These data sustain the theory that the better clinical efficacy of methotrexate in patients with psoriasis might be due to the more pronounced inhibition of important enzymes such as the enzymes of the pentose phosphate shunt.

Acid Phosphatase↗
PubMed1975

Regulated in vitro synthesis of the enzymes of the deo operon of Escerichia coli. properties of the DNA directed system.

The four enzymes deoxyriboaldolase, thymidine phosporylase, deoxyribomutase, and purine nucleoside phosphorylase have been synthesized in substantial amounts in a DNA-dependent in vitro system programmed with DNA containing the deo operon. The synthesis is greatly stimulated by deoxyribose-5-phosphate and cyclic AMP indicating that the deoR repressor and the catabolite activating protein (CAP) are highly active under our cell-free conditions. In contrast it has not yet been possible to observe a reproducible effect of the cytR repressor in vitro. The sequential appearance of active enzymes has confirmed the direction of transcription as being dra-tpp-drm-pup and has indicated that the four genes are transcribed into a single tetracistronic message.

Aldehyde-Lyases↗
PubMed1982

Setaria cervi: enzymes in microfilariae and in vitro action of antifilarials.

Microfilariae of bovine filarial parasite Setaria cervi are equipped with the enzymes of glycolysis, pentose phosphate and PEP-succinate pathways and thus resemble the adult form in its metabolic pattern. Malate dehydrogenase was the most active enzyme in microfilariae followed by lactic dehydrogenase and fumarase, while phosphoglucoisomerase, PEP-carboxykinase and FDP-aldolase were comparatively less active. The very low ratio of PK/PEPCK in S. cervi microfilariae indicates active fixation of CO2 into PEP to produce oxalacetate. Centperazine and diethylcarbamazine significantly inhibited PEP-carboxykinase, fumarate reductase and succinic dehydrogenase, suggesting that these antifilarials probably exert microfilaricidal action by blocking the PEP-succinate pathway.

Animals↗
PubMed1977

Increased intracellular phosphoribosylpyrophosphate and accelerated orotic acid decarboxylation in a mouse cell line resistant to purine and pyrimidine ribonucleosides.

A line of mouse fibroblasts (A9AU-1), originally selected for growth in the presence of 6-azauridine, has been found to be resistant to cytotoxic concentrations of adenosine, guanosine, and thymidine. A9AU-1 cells convert orotic acid to uridine 5'-monophosphate at twice the rate of the A9P line from which the A9AU-1 clone was selected. The resistant cells also excrete purines, synthesized de novo, into the medium at an increased velocity. The average intracellular 5-phosphoribosyl-1-pyrophosphate (PRPP) concentration of the resistant line is 45% higher than that of the parental line. The elevated PRPP concentration is likely to be responsible for both the apparent acceleration of pyrimidine synthesis and the increased excretion of purines into the growth medium; it might also account, by one of the several possible mechanisms, for the resistance of the cells to cytotoxic concentrations of the various nucleosides.

Adenine Phosphoribosyltransferase↗
PubMed1977

The control of cell proliferation by preformed purines: a genetic study. II. Pleiotropic manifestations and mechanism of a control exerted by adenylic purines on PRPP synthesis.

When plated in medium containing 0.5 microgram/ml coformycin and adenosine (or adenine) fibroblasts were killed, even if pyrimidines were supplied. Measurements of N-formylglycine amide ribonucleotide synthesis showed that lethality is a manifestation of purine starvation. In the case of adenosine kinase deficient cells, growth was restored by hypoxanthine. The adenylic derivatives block only purine biosynthesis, presumably by inhibition of PRPP-amidotransferase. In this same medium, wild-type cells exhibited symptoms of PRPP deprivation: purine and pyrimidine syntheses were both shut off and HGPRT was simultaneously inactivated. The pleiotropic control by adenosine was abolished in adenosine-resistant mutants that behaved as PRPP "over-producers." These mutations conferred partial resistance to various toxic purine and pyrimidine analogs and preserved HGPRT activity in adenosine-containing medium. This permits selection against these mutants. Evidence suggesting that adenosine kinase products may fulfill a specific function in the regulation of PRPP synthesis is discussed.

Adenine↗
PubMed1978

Purine reutilization and synthesis de novo in long-term human lymphocyte cell lines deficient in adenine phosphoribosyltransferase activity.

Clonal lines, with either partial or total deficiency of adenine phosphoribosyltransferase (APRT) were derived from the WI-L2 long-term human lymphocyte line by selection for resistance to the adenine analogs 8-azaadenine or 2,6-diaminopurine. Resistance to 8-azaadenine also conferred resistance to 2,6 diaminopurine and vice versa. Cells with 30--40% of wild-type APRT activity were selected by resistance to 0.01 mM 2,6-diaminopurine or 1.40 mM 8-azaadenine. The APRT in the 8-azaadinine-resistant cells exhibited a four- to sevenfold increase in the apparent Km for adenine. Activities of three other purine reutilization and interconversion enzymes in the resistant cells, including hypoxanthine phosphoribosyltransferase (HPRT), adenosine kinase, and adenosine deaminase, were within the range of wild-type activities. The doubling times of the APRT-deficient cells in purine-free medium was not different from wild-type cells. The APRT in the 8-azaadenine-resistant cells did not have an altered mobility in glycerol gradients as compared to wild-type cells. The rate of purine synthesis de novo and intracellular levels of 5-phosphoribosyl-1-pyrophosphate were unchanged in the APRT-deficient cells as compared to WI-L2. The ability of the cells to reutilize exogenous adenine, however, was severely impaired.

Adenine↗