Monensin, a monovalent ion-selective ionophore, facilitates the transmembrane exchange of principally sodium ions for protons. The outer surface of the ionophore-ion complex is composed largely of nonpolar hydrocarbon, which imparts a high solubility to the complexes in nonpolar solvents. In biological systems, these complexes are freely soluble in the lipid components of membranes and, presumably, diffuse or shuttle through the membranes from one aqueous membrane interface to the other. The net effect for monensin is a trans-membrane exchange of sodium ions for protons. However, the interaction of an ionophore with biological membranes, and its ionophoric expression, is highly dependent on the biochemical configuration of the membrane itself. One apparent consequence of this exchange is the neutralization of acidic intracellular compartments such as the trans Golgi apparatus cisternae and associated elements, lysosomes, and certain endosomes. This is accompanied by a disruption of trans Golgi apparatus cisternae and of lysosome and acidic endosome function. At the same time, Golgi apparatus cisternae appear to swell, presumably due to osmotic uptake of water resulting from the inward movement of ions. Monensin effects on Golgi apparatus are observed in cells from a wide range of plant and animal species. The action of monensin is most often exerted on the trans half of the stacked cisternae, often near the point of exit of secretory vesicles at the trans face of the stacked cisternae, or, especially at low monensin concentrations or short exposure times, near the middle of the stacked cisternae. The effects of monensin are quite rapid in both animal and plant cells; i.e., changes in Golgi apparatus may be observed after only 2-5 min of exposure. It is implicit in these observations that the uptake of osmotically active cations is accompanied by a concomitant efflux of H+ and that a net influx of protons would be required to sustain the ionic exchange long enough to account for the swelling of cisternae observed in electron micrographs. In the Golgi apparatus, late processing events such as terminal glycosylation and proteolytic cleavages are most susceptible to inhibition by monensin. Yet, many incompletely processed molecules may still be secreted via yet poorly understood mechanisms that appear to bypass the Golgi apparatus. In endocytosis, monensin does not prevent internalization. However, intracellular degradation of internalized ligands may be prevented.(ABSTRACT TRUNCATED AT 400 WORDS)

A hormone-and growth factor-stimulated NADH oxidase of the mammalian plasma membrane, constitutively activated in transformed cells, was inhibited preferentially in HeLa, ovarian carcinoma, mammary adenocarcinoma, and HL-60 cells, all of human origin, by the naturally occurring quinone analog capsaicin (8-methyl-N-vanillyl-6- Previous reports described a growth factor-and hormonestimulated NADH oxidase activity of rat liver plasma membranes (1, 2). Several correlative studies have produced evidence for the involvement of this growth factor-responsive NADH oxidase in the control of cell proliferation (3). The activity in transformed cells and tissues was distinguished from that of liver in that the growth factor and hormone responsiveness was lost in plasma membranes of transformed liver tissues. These studies were done with hyperplastic nodules of liver induced by the liver carcinogen 2-acetylaminofluorene (4) and with transplanted rat hepatomas (5).The NADH oxidase activity of liver plasma membranes is unique among oxidoreductase activities not only in its response to growth factors and hormones but also in its response to inhibitors and activators other than growth factors and hormones (3, 6, 7). To further characterize this unusual NADH oxidase activity, studies were extended to include responses to quinone analogs. The activity has been shown to require quinones (8) but has been little characterized with respect to response to potentially inhibitory quinone analogs such as capsaicin (8-methyl-N-vanillyl-6-noneamide).The NADH oxidase activity of rat liver plasma membrane was largely unaffected by capsaicin, whereas the NADH oxidase activity of HeLa plasma membranes was strongly inhibited. The results indicate a fundamental difference in response to capsaicin between the NADH oxidase activity of normal and transformed cells and tissues that correlates with inhibition of growth and induction of apoptosis in the transformed cells.

NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide interchange and exhibit prion-like properties. The two enzymatic activities alternate to generate a regular period length of about 24 min. Here we report the expression, cloning, and characterization of a tumor-associated NADH oxidase (tNOX). The cDNA sequence of 1830 bp is located on gene Xq25-26 with an open reading frame encoding 610 amino acids. The activities of the bacterially expressed tNOX oscillate with a period length of 22 min as is characteristic of tNOX activities in situ. The activities are inhibited completely by capsaicin, which represents a defining characteristic of tNOX activity. Functional motifs identified by site-directed mutagenesis within the C-terminal portion of the tNOX protein corresponding to the processed plasma membrane-associated form include quinone (capsaicin), copper and adenine nucleotide binding domains, and two cysteines essential for catalytic activity. Four of the six cysteine to alanine replacements retained enzymatic activity, but the period lengths of the oscillations were increased. A single protein with two alternating enzymatic activities indicative of a time-keeping function is unprecedented in the biochemical literature.

Currently there is wide interest in the medicinal benefits of green tea (Camellia sinensis). Tea is one of the most widely consumed beverages in the world, and extracts of tea leaves are also sold as dietary supplements. Green tea extracts contain a unique set of catechins that possess biologic activity in antioxidant, antiangiogenesis, and antiproliferative assays that are potentially relevant to the prevention and treatment of various forms of cancer. With the increasing interest in the health properties of tea and a significant rise in their scientific investigation, it is the aim of this review to summarize recent findings on the anticancer and medicinal properties of green tea, focusing on the biologic properties of the major tea catechin, (-)-epigallocatechin and its antitumor properties.

Abstract. The transfer of membranes from the endoplasmic reticulum to the Golgi apparatus occurs via 50-70 nm transition vesicles which derive from partrough, part-smooth transitional elements of the endoplasmic reticulum (TER). Vesicle budding from the TER is an ATP-dependent process both in vivo and in vitro. An ATPase with a monomer molecular weight of 100 kD by SDS-PAGE has been isolated from TER and designated as TER ATPase. The native TER ATPase has been characterized as a hexamer of six 100-kD subunits by gel filtration. The protein catalyzes the hydrolysis of [732-P]ATP and is phosphorylated in the presence of Mg 2÷. It is distinct from the classical transport ATPases based on pH optima, ion effects, and inhibitor specificity. Electron microscopy of negatively stained preparations revealed the TER ATPase to be a ring-shaped structure with sixfold rotational symmetry. A 19-amino acid sequence of TER ATPase having 84 % identity with valosincontaining protein and 64% identity with a yeast cellcycle control protein CDC48p was obtained. Antisynthetic peptide antisera to a 15-amino acid portion of the sequence of TER ATPase recognized a 100-kD protein from TER. These antisera reduced the ATPdependent cell-free formation of transition vesicles from isolated TER of rat liver. In a reconstituted membrane transfer system, TER ATPase antisera inhibited transfer of radiolabeled material from endoplasmic reticulum to Golgi apparatus, while preimmune sera did not. The results suggest that the TER ATPase is obligatorily involved in the ATP requirements for budding of transition vesicles from the TER. cDNA clones encoding TER ATPase were isolated by immunoscreening a rat liver cDNA library with the afffinity-purified TER ATPase antibody. A computer search of deduced amino acid sequences revealed the cloned TER ATPase to be the rat equivalent of porcine valosin-containing protein, a member of a novel family of ATP binding, homo-oligomeric proteins including the N-ethylmaleimide-sensitive fusion protein.