title: 5'-Nucleotide phosphodiesterase and alkaline phosphatase in tumor cells: evidence for existence of novel species in the cytosol.
abstract: Characteristics of 5'-nucleotide phosphodiesterase (phosphodiesterase I, EC 3.1.4.1) and alkaline phosphatase (EC 3.1.3.1) activities in tumor cell lines of human and murine origin were examined. Of the 15 cell lines tested, 5'-nucleotide phosphodiesterase activity in 13 cell lines and alkaline phosphatase activity in 10 cell lines were inhibited by N-ethylmaleimide and activated by dithiothreitol (N-ethylmaleimide-sensitive), and suggested to be SH-enzymes. In contrast, the two phosphohydrolases from normal tissues were inactivated by dithiothreitol, but not by N-ethylmaleimide (dithiothreitol-sensitive). There was only one tumor cell line in which both activities were dithiothreitol-sensitive. Human hepatoma PLC/PRF/5 cells appear to possess both types of 5'-nucleotide phosphodiesterase and alkaline phosphatase, and the subcellular distribution of these enzymes in this cell line was investigated. Dithiothreitol-sensitive 5'-nucleotide phosphodiesterase and alkaline phosphatase of PLC/PRF/5 cells were localized in the plasma membrane as in normal tissues, but N-ethylmaleimide-sensitive phosphohydrolases were soluble cytosolic proteins. N-Ethylmaleimide-sensitive 5'-nucleotide phosphodiesterase and alkaline phosphatase activities from other cell lines were also recovered in the cytosol. Molecular masses of cytosolic N-ethylmaleimide-sensitive phosphohydrolases were apparently smaller than their membrane-bound dithiothreitol-sensitive counterparts, as judged from gel filtration. It was concluded that many tumor cell lines lack plasma membrane 5'-nucleotide phosphodiesterase and alkaline phosphatase, but express enzymes with similar activities in the cytosol, with properties clearly distinguishable from enzymes so far characterized.
authors.affiliation: Institute of Applied Microbiology, University of Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Fukazawa
authors.forename: T
authors.initials: T
authors.lastname: Nishimura
authors.forename: N
authors.initials: N
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D004229:Dithiothreitol / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005033:Ethylmaleimide / Q000494:pharmacology; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D051379:Mice; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology*; D014461:Ultracentrifugation
chemical_list: D002087:Butyrates; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases; D043264:Phosphodiesterase I; D005033:Ethylmaleimide; D004229:Dithiothreitol