Inhibition of 5′-nucleotidase from Ehrlich ascites-tumour cells by nucleoside triphosphates

1. 5'-Nucleotidase activity was obtained in a soluble form after treatment of a particulate fraction from Ehrlich ascites-tumour cells with deoxycholate. The relative rates of hydrolysis of 6-thioinosine 5'-phosphate, UMP, AMP, CMP, GMP, IMP, xanthosine monophosphate, thymidine monophosphate and 2',3'-AMP were 180, 129, 100, 93, 83, 79, 46, 41 and 3 respectively. 2. Values found for the Michaelis constant were: AMP, 67+/-12mum; IMP, 111+/-8mum; GMP, 93mum. 3. ATP and thymidine triphosphate were competitive inhibitors of AMP hydrolysis (inhibitor constants 0.4 and 4.8mum respectively); UTP, GTP and CTP were mixed competitive and non-competitive inhibitors. Thymidine triphosphate was a competitive inhibitor of IMP hydrolysis (inhibitor constant 14.4mum) and ATP, UTP and GTP showed mixed competitive and non-competitive inhibition. 4. ATP, thymidine triphosphate, UTP, GTP and CTP did not completely inhibit hydrolysis of AMP, IMP and UMP; the concentrations of ATP required to inhibit AMP and IMP hydrolysis by 50% were 12 and 230mum respectively. 5. Non-hyperbolic curves relating activity to UMP concentration were obtained in the presence and absence of triphosphates. 6. After fractionation on Sephadex G-200 columns a single peak of 5'-nucleotidase activity (particle weight 120000-125000) was obtained with AMP, IMP and GMP as substrates. UMP hydrolysis was catalysed by enzyme in this peak and in two slower peaks corresponding to apparent particle weights of 32000 and 16000; a single component (particle weight 120000), reacting with UMP and insensitive to UTP inhibition, was obtained when the column was eluted with buffer containing 1mm-UMP. 7. The possible significance of the results in the regulation of tumour-cell 5'-nucleotidase is discussed.     

Solid intraperitoneal Landschütz tumour in mice: implications in cancer chemotherapy and immunology studies.

Multiple intraperitoneal injections of various normal sera into BALB/c mice inoculated intraperitoneally with Landschütz ascites tumour cells abrogated the development of ascitic syndrome in almost all the animals. In a large proportion of the survivors solid intraperitoneal tumours developed, composed of characteristic ascites tumour cells engulfed and encapsulated in connective tissue. The effect of serum on the development of the solid tumour was diminished if the donor had been immunized against mouse IgG. Inoculated animals treated with serum hyperimmune against mouse IgG showed accelerated ascitic tumour growth. Cyclophosphamide or arabinosylcytosine strongly inhibited growth of solid tumours. Simultaneous administration of arabinosylcytosine and its antagonist cycloheximide did not interrupt tumour growth.     

Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Flora von Olmütz

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Phycobilisome from Anabaena Variabilis Kütz. and its Model Conjugates

The model conjugates phycocyanin-allophycocyanin (C-PC-APC) and phycoerythrocyanin-phycocyanin-allophycocyanin (PEC-C-PC-APC) were synthesized by using a heterobifunctional coupling reagent N-succinimidyl-3-(2-pyridyldithio)propionate. The rod-core complex (αβ)₆ ^PCL_RC ²⁷(αβ)₃ ^APCL_C ^8.9 and phycobilisomes were separated from Anabaena variabilis. Energy transfer features for the conjugates and the complexes were compared. The absorption and fluorescence emission spectra indicated that the linker-peptides mediate interaction of phycobiliproteins and prompt energy transfer. The energy transfer in the conjugates was detected by fluorescence emission spectra and confirmed by the addition of dithiothreitol. The conjugates may be used as models for studying the energy transfer mechanism in phycobilisomes. This revised version was published online in September 2006 with corrections to the Cover Date.