Bands of detergent-resistant membrane fractions in sucrose gradients after ultracentrifugation. Boar sperm cells were incubated with detergents for 30 min at 4°C, membrane fractions were mechanically detached and separated from the remaining cell pellet by centrifugation. The supernatant was transferred under a continuous sucrose gradient for subsequent flotation. The obtained density gradient is additionally shown at the right of the figure. For further details see the Materials and Methods section.