Subcellular distribution and electrophoretic behavior of aminopeptidase in human placenta.

The activity of aminopeptidase was found by differential centrifugation to be distributed in the three main subcellular sites of human placenta: the lysosomal-mitochondrial, microsomal, and supernatant fractions. Placental lysosomes were isolated from the lysosomal-mitochondrial fraction and identified by electron microscopy. The lysosomal and microsomal aminopeptidases presented different electrophoretic patterns, suggested the existence of multiple molecular forms of aminopeptidase within the human placenta. Serum aminopeptidase appearing during pregnancy showed the same bands as those of the lysosomal enzyme. This finding suggests that the increased aminopeptidase in pregnancy serum may originate from the lysosomes of the placenta. Placental aminopeptidase bands were absent in fetal serum. The supernatant contained most of the total activity, which turned out to be due to contamination of this fraction by retroplacental blood.