Chapter 7: Microsomes

7.1 Lysosome Isolation in Isotonic Sucrose

MATERIALS

• Rat liver
  
• Physiological saline (0.85% w/v NaCl)
  
• 0.25 M sucrose in 10 mM Tris-HCL, pH 7.4
  
• Brendler teflon homogenizer
  
• Refrigerated preparative centrifuge
  
• 0.08 M CaCl in 0.25 M sucrose plus 10 mM Tris-HCl
  
• 150 mM KCl in 10 mM Tris-HCl Buffer, pH 7.4
  
• Phase contrast microscope, slides, coverslips

PROCEDURE 4

1. Decapitate and exsanguinate a rat that has been starved for at least 24 hours prior to the lab. 5

   Fill a syringe with saline and gently perfuse the liver by forcing the saline through the hepatic portal vein, and through the liver.

2. Remove the liver, place it in a preweighed beaker and weigh the beaker and liver. Calculate the weight of the liver.

3. Prepare a 10% (w/v) homogenate or brei. For each gram of liver, add 9.0 ml of 0.25 M sucrose in 10 mM Tris-HCL, pH 7.4. to the beaker.

4. Gently chop the liver in the sucrose and transfer the chopped liver to a teflon homogenizer. 6

   Gently homogenize the liver while keeping it chilled.

5. Centrifuge the brei at 12,000 xg for 10 minutes at 4 ° C. Decant the supernatant into a chilled beaker and discard the pellet.

6. Add 0.08 M CaCl to the supernatant to yield a final concentration of 8 mM (use 1 ml of CaCl per 9 ml of supernatant). Stir gently and recentrifuge at 25,000 xg for 15 minutes at 4 ° C

7. Carefully remove and discard the supernatant. 7

8. Resuspend the pellet (containing the lysosomes) in 30 ml of 150 mM KCl in 10 mM Tris-HCl Buffer, pH 7.4.

9. Re-sediment the lysosomes by a final centrifugation at 25,000 xg for 15 minutes at 4 ° C.

10. Remove a small portion of the pellet for Exercise 7.2. Resuspend the remainder of the pellet in 30 ml of 150 mM KCl/10 mM Tris-HCl Buffer. This suspension is the lysosome fraction for Exercise 7.3.

11. Prepare a wet mount of the resuspended lysosome pellet and observe with a phase contrast microscope at 100X. Draw any structures observed.