Entrapment into liposomes of fusicoccin binding sites

Fusicoccin (FC) binding sites solubilised from microsomal fractions of spinach leaves have been entrapped into soybean lecithin liposomes with an 80% yield. The investigation of the properties of these proteoliposomes has demonstrated that the rates of FC-binding and of exchange between radioactive and cold FC are intermediate between those observed with membrane-bound and with solubilised binding sites. It appears that the entrapped proteins are preferentially outside-oriented since they are inactivated by trypsin treatment; moreover, Triton X-100 permeabilization of the proteoliposomes demonstrated that one fifth of these sites are inside-oriented.