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Variation in microsomal subfractions obtained from normal animal tissues and transformed cells following cell
Abstract:
Microsomal membranes were obtained from MPC-11 cells, L-cells, Krebs II ascites cells and various normal animal tissues following cell disruption by nitrogen cavitation. Membrane preparations were applied to discontinuous sucrose gradients designed to separate three fractions--heavy rough (HR), light rough (LR) and smooth (S) microsomes. In each of the transformed cell lines all three fractions were found whilst in the normal tissues tested the HR fraction was absent. Of the normal tissues liver and pancreas were rich in both LR and S microsomes, the presence of large amounts of LR indicating a rich protein synthesizing activity on membrane-bound polysomes. Kidney also contained appreciable LR but much less than both liver and pancreas. Both heart and lung contained virtually only S microsomal material--a reflection of low protein synthetic activity on membrane-bound polysomes. Attempts to promote the appearance of the HR fraction in liver, kidney and pancreas by incubation in tissue culture medium, or, in the case of pancreas, by cholecystokinin/pancreozymin/secretin stimulation both in vivo and in vitro were unsuccessful.
Insights
Transformed cell lines possess heavy rough (HR) microsomes, unlike normal tissues. Normal tissues show varying levels of light rough (LR) and smooth (S) microsomes, reflecting protein synthesis activity.
Area of Science:
- Cell Biology
- Biochemistry
Background:
- Microsomal membranes are crucial cellular components involved in protein synthesis and modification.
- Differentiation between heavy rough (HR), light rough (LR), and smooth (S) microsomes is based on their density and associated polysomes.
Purpose of the Study:
- To investigate the presence and distribution of different microsomal fractions (HR, LR, S) in transformed cell lines versus normal animal tissues.
- To correlate microsomal fraction composition with cellular protein synthesis activity.
Main Methods:
- Microsomal membranes were isolated from various cell lines (MPC-11, L-cells, Krebs II ascites) and normal animal tissues using nitrogen cavitation.
- Membrane preparations were fractionated using discontinuous sucrose gradients to separate HR, LR, and S microsomes.
Main Results:
- Transformed cell lines contained all three microsomal fractions (HR, LR, S).
- Normal tissues lacked the HR fraction.
- Liver and pancreas showed abundant LR and S microsomes, indicating high protein synthesis.
- Kidney had moderate LR, while heart and lung primarily contained S microsomes, suggesting lower protein synthesis.
Conclusions:
- The presence of HR microsomes is a characteristic feature of transformed cells, absent in normal tissues.
- Microsomal fraction composition in normal tissues correlates with their known protein synthesis activities.
- Experimental attempts to induce HR fraction formation in normal tissues were unsuccessful.