@entity134 metabolizing enzymes associated with the microvillar membrane of XXXX placenta.

@entity172 @entity1 @entity18333 @entity14024 @entity19517 @entity6041 @entity19674 @entity1219 @entity1815 @entity653 @entity53 @entity134 @entity6173 @entity2421 @entity2975 @entity9027 @entity230
17 beta-Hydroxysteroid oxidoreductase, as well as @entity19517 and @entity9027 sulfatases, were found in the plasma membrane of microvilli of the fetal syncytiotrophoblast. Because of their location, these enzymes may influence feto-maternal transfer of @entity230 circulating as @entity14024 , the utilization of sulfated @entity172 precursors and the proportion of @entity1815 and @entity53 delivered towards fetal and maternal circulations. Microvillar vesicles isolated from @entity1 term placentas were @entity2421 medium to obtain a membrane preparation. A fraction of the @entity53 17 beta-oxidoreductase ( @entity18333 ) activity in the vesicle remained associated to the membrane after disruption and treatment with 2 M @entity1219 . The membrane-associated activity was resistant to inhibition with trypsin and did not react with a polyclonal antibody which neutralized cytosolic @entity18333 activity. The membrane-associated enzyme was solubilized with a @entity6041 - @entity653 buffer solution and purified on Sephadex G-100. The estimated molecular weight of the solubilized enzyme (137 kDa) appears to correspond to a tetramer since it was found to be about twice the size of the cytosolic enzyme. Both enzymes focused in @entity2975 gels at pH 5.2. The Km relative to E2 of the membrane-associated @entity18333 (1.3 microM) differs from those of mitochondrial (0.43 microM), microsomal (0.69 microM) and cytosolic (11 microM) fractions. The cytosolic and the microvillar membrane associated @entity19674 oxidoreductases also differ in their specificity for @entity6173 and C19 @entity134 substrates and in their pH dependence patterns. Sulfatases acting on @entity19517 and @entity9027 in microvillar membranes were insensitive to trypsin and as resistant to washes with 2 M @entity1219 as alkaline phosphatase. This data indicated that @entity134 sulfatases are also microvillar membrane associated enzymes of potential physiologic importance in the hydrolysis of @entity172 precursors.
