Examination of different preparations of human placental plasma membrane for the binding of insulin, transferrin and immunoglobulins

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Abstract
Plasma membrane was prepared from human placental tissue by 2 standard methods. The preparations, termed placental villous surface membrane [PVM] and placental plasma membrane [PPM] examined by EM and polyacrylamide gel electrophoresis, were characterized with respect to their binding properties for insulin, transferrin, .alpha.2-macroglobulin and IgM and IgG1. By means of sucrose density-gradient centrifugation, it was possible to fractionate the PVM into 2 distinct fractions. The 1st fraction, under the conditions used, was heavier (density > 1.080 g.cntdot.cm-3) and was obtained as a pellet. It bound transferrin and IgM and had low specific activities for 5''-nucleotidase and for the binding of IgG1. The lighter fraction (density range 1.048-1.050 g.cntdot.cm-3) had a high specific activity for 5''-nucleotidase and for IgG1 binding. Transferrin and IgM did not bind to this fraction. Insulin bound to both the fractions with comparable levels of specific binding activity, while .alpha.2-macroglobulin binding was undetectable. The PPM preparation had binding properties similar to those of the light fraction of PVM.