PREDOMINANT EXPRESSION OF THE BETA-SUBUNIT OF PROLYL 4-HYDROXYLASE (DISULFIDE-ISOMERASE) IN HUMAN EXTRAVILLOUS TROPHOBLASTS

Prolyl 4-hydroxylase is a heterodimeric enzyme that is crucial in the biosynthesis of collagen. The beta subunit of this enzyme is a multifu nctional protein which is also known as protein-disulfide isomerase. I mmunofluorescence and monoclonal antibody (Mab) 5B5 were used to local ize the beta subunit in human extraembryonic tissues. The strongest si tes of 5B5 reactivity were extravillous cytotrophoblasts in the basal plate. uteroplacental arteries and amniochorion, syncytiotrophoblast d isplayed variable weaker reactivity. Only a small fraction of placenta l 5B5 antigen was detected as a component of prolyl-4-hydroxylase by a ffinity chromatography on immobilized polyproline. The results indicat e a difference in the expression of an endoplasmic reticulum marker be tween villous and extravillous trophoblast. The predominance of 5B5 an tigen in extravillous trophoblast could be associated with an increase d ability to synthesize collagen or other enzymatic reactions associat ed with prolyl 4-hydroxylase beta subunit.