Activation homogenates, intact cellular

In contrast, we did not find these concentration-dependent qualitative changes when activation occurred in intact cellular systems (16). We examined the adducts formed in mouse embryo cells in culture and in mouse skin ijri vivo over 40- and 100-fold DMBA concentration ranges, respectively, and found quantitative, but no qualitative, changes in binding (16). At all concentrations, activation appeared to be through the bay region dihydrodiol epoxide pathway. The cellular systems are physically very different from the homogenate systems and it is difficult to... 

Effects of dopaminergic antagonists on dopamine-stimulated cAMP accumulation, adenylate cyclase activity, and calmodulin-stimulated phosphodiesterase (PDE) activity in intact bovine parathyroid cells or cellular homogenates. Values for or IC50 are given as uM. NT, not tested. 

The membrane is a delicate yet sturdy structure which must be studied intact but cannot be isolated without disruption. In essence, membrane isolation involves the removal of all other parts of the cell. The purity of a membrane preparation is usually measured by the relative increase in specific activity of a membrane-boimd marker enzyme in the membrane preparation over the specific activity of the marker enzyme in the homogenate. In cases where specific membrane markers are lacking, enzymatic activities associated exclusively or primarily with other subcellular components must be demonstrated to be absent in order to show the preparation free from cellular contaminants. Such data, combined with phase-contrast and electron microscopic images of the preparation, are usually accepted as adequate criteria for the measurement of purity. One additional technique, at least for membranes with antigenic properties, is preparation of fluorescent antibodies to the isolated membranes and observation of the antibody localization in whole cells (Kabat and Meyer, 1971). The use of fluorescent probes in determining membrane structure and function has been reviewed (Radda, 1975 Azzi, 1975). 

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