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Some aspects of the ultrastructure and enzyme cytochemistry of normal and virus-transformed cells

By Alan Leslie Dawson


Morphological and hydrolytic enzyme cytochemical investigations have been applied to three normal and transformed cell systems in order to relate changes in hydrolytic enzyme activity to changes in ultrastructural organisation occurring when normal cells in vitro are transformed by tumour virus.\ud \ud On transformation changes in cell shape, growth and social behaviour are detected with the light microscope. At the ultrastructural level the major changes are in the extent of the GERL (Golgi, endoplasmic reticulum, lysosome) systems and are likely to be in response to altered rates of entry of metabolites through the cell membrane caused by transformation-dependent modifications of the cell surface.\ud \ud Five hydrolytic enzymes are demonstrated by light microscopic enzyme cytochemistryi mainly by azo-dye methods. Differences in levels of activity are difficult to assess visually but microdensitometry shows that transformed 3T3 cells have higher acid phosphatase activity than normal cells. This is confirmed by biochemical assays which also show that, unlike acid phosphatase, glucosaminidase has higher activity in normal cells. Biochemistry additionally provides a means of studying the effect of glutaraldehyde fixation on enzyme activity.\ud \ud Azo-dye techniques are found to be unsuitable for use in electron microscopic enzyme cytochemistry since dye is lost from cultured cells during processing and end product-like deposits appear in secondary lysosomes of control material. This latter phenomenon is investigated in other tissues. Metal-salt methods are, therefore, utilised for the demonstration of three enzymes, activity being largely confined to Golgi elements and lysosomes. Some activity is localised at the cell surface and this lends support to the possibility of surface modification through a process of sublethal autolysis by lysosomal enzymes. Examination of GERL morphology and enzyme activity gives an insight into the functioning of the system and provides evidence of possible mechanisms of cellular autophagy

Topics: QD
Year: 1976
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