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

ALVAREZ, C

BIOCHIMICA ET BIOPHYSICA ACTA-PROTEIN STRUCTURE AND MOLECULAR ENZYMOLOGY

Elsevier

Año: 1994 vol. 1207 p. 102 - 102

0167-4838

he membrane-bound enzyme 3β-hydroxysteroid dehydrogenase Δ^5-4 isomerase (3β-HSD) catalyzes the formation of Δ⁴-3-ketosteroids from Δ⁵-3β-hydroxysteroids in placental, adrenal, testicular and ovarian tissues. In the present study was investigated the transverse-plane topography of 3β-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 bein