Topic overview

Start with the big picture

Fractionation begins with mechanical disruption of tissue in cold, isotonic conditions, followed by differential centrifugation. Successive spins produce pellets containing components such as nuclei, mitochondria and microsomes, while smaller material remains in the supernatant. Density gradients, including sucrose or Percoll, can further separate organelles with similar sizes but different buoyant densities. Marker enzymes and other markers help identify the organelles present: examples include citrate synthase for the mitochondrial matrix, acid phosphatase for lysosomes, catalase for peroxisomes, and lactate dehydrogenase for cytosol. Enzyme activity assays and methods such as Western blotting can assess enrichment and contamination. Interpreting these findings requires attention to sample handling, since organelle damage or carryover can affect apparent fraction purity.