Topography of human placental 3beta-hydroxysteroid dehydrogenase /5-4 steroid isomerase in microsomal membrane. A study using limited proteolysis and immunoblotting

ALVAREZ CECILIA; GENTI DE RAIMONDI SUSANA; PATRITO LUIS; FLURY ALFREDO

Elsevier

Año: 1994 vol. 1207 p. 102 - 102

he membrane-bound enzyme 3/3-hydroxysteroid dehydrogenase A 54 isomerase (3/3-HSD) catalyzes the formation of A4-3-keto - steroids from AS-3/3-hydroxysteroids in placental, adrenal, testicular and ovarian tissues. In the present study was investigated the transverse-plane topography of 3/3-HSD within the human placental microsome membranes employing immune-replica analysis in combination with surface specific proteolysis. The crucial domains of the enzyme for the dehydrogenase and isomerase reactions are inactivated by proteinase treatments under conditions where latency of hexose-6-phosphate dehydrogenase was 95%. The data indicate that these crucial domains face the cytosolic side of the endoplasmic reticulum membrane. Incubation of the intact microsomes with trypsin produces several immune reactive fragments ranging from 29 to 11 kDa in addition to 42 kDa native enzyme, one of them being shielded by the membrane structure and/or by other intrinsic and peripheral membrane pro