Studies on N-acetal-beta-D-hexosaminidases in human placenta

Abstract

The distribution, biosynthesis and secretion of multiple forms of N-acetyl-B-D-hexosaminidase have been studied in first trimester and term human placentas. Hexosaminidases A, B, I1 and were identified in extracts from whole term placental tissue and the major multiple forms, A and B, were purified 1400-fold and 1000-fold, respectively. Antisera raised to purified hexosaminidase A and B cross-reacted with the A, B, I1 and I2 forms and confirmed their structural relatedness. Total hexosaminidase specific activities and multiple form profiles were compared in well-defined anatomical regions of first trimester and term placentas. Most regions showed a decrease in specific activity with gestation except for the chorion laeve and umbilical cord which showed an increase and no change, respectively. The profiles differed both with respect to placental region and developmental stage. A placental slice system was used to study the biosynthesis and secretion of hexosaminidase in vitro. Evidence for the de novo synthesis of hexosaminidase was obtained by immunological isolation and analysis of radiolabelled enzyme. Comparative studies showed that rates of hexosaminidase and total protein synthesis were greater in first trimester than term placental villi. Hexosaminidase was secreted into the incubation medium by slices from first trimester and term placental villi, chorion laeve and amnion. Differences in the amount of enzyme and in the nature of the multiple forms secreted were found both with respect to placental region and developmental stage. The low levels of secreted suggested that the placenta was unlikely to provide the major source of elevated levels in pregnancy serum. Inhibitor studies suggested the involvement of microtubules and microfilaments in the secretion of hexosaminidase from placental villi. Hexosaminidase mRNA was identified in the poly (A)-containing RNA isolated from term placental total RNA preparations. mRNAs coding for the [alpha] and [beta] subunit polypeptides have been tentatively identified using anti-(hexosaminidase B) and specific anti-(hexosaminidase A) prepared by the absorption of anti-(hexosaminidase A) with hexosaminidase B.