Reaction of anti‐phosphatidyl inositol antisera with neural membranes

Ca. 15% of the phosphatidyl inositol in myelin and microsomal membranes from rat brain was detectable by antiphosphatidyl inositol antibody. Antibody-detectable phosphatidyl inositol in myelin and microsomes readily increased when the membranes were incubated at 45 C with the antiserum. Synaptic membranes also had only a limited capacity to adsorb antibody. Quantitative binding studies with synaptic membranes and mitochondria were limited, because these membranes contain cardiolipin, which cross reacts with phosphatidyl inositol antisera. Moreover, highly purified synaptic and mitochondrial membranes contain appreciable amounts of other membrane fractions.