Membrane bound share of the 15-LOX depends on the calcium concentration in the incubation mixture. The purified rabbit 15-LOX (30 nkat/mL) was incubated for 5 minutes with SMP (1 mg/mL) in the presence of different calcium concentrations. The membranes were spun down and the 15-LOX was determined in the supernatant by immunoblot analysis. The blots were quantified with a Phoretix 1D Standard program. The LOX content in the control incubation (no membranes) was set at 100%.