Secretion and biosynthesis of N-acetyl-beta-D-hexosaminidases by human placental tissues in vitro

Chorionic villi selectively secrete the B isoenzyme and, to a lesser extent, the A isoenzyme of lysosomal beta-hexosaminidase when incubated in vitro, suggesting that this tissue could contribute to maternal serum beta-hexosaminidase B and A activities in vivo. The results make it unlikely, however, that the placenta is the source of the I2 isoenzyme found in maternal serum. Samples of amnion and term chorion laeve secreted predominantly the B isoenzyme whereas first-trimester chorion laeve secreted the A, B and I2 isoenzymes. Amnion and chorion laeve may, therefore, be a source of the A, B and I2 activities found in amniotic fluid. Chorionic villi supported the cycloheximide-sensitive incorporation of [3H]leucine into immunoreactive beta-hexosaminidase thereby providing direct evidence for enzyme biosynthesis. Newly synthesized beta-hexosaminidase was detectable in the medium only after extended incubation and the secretion of beta-hexosaminidase activity continued at normal rates for several hours in the absence of protein synthesis. These results indicate that enzyme synthesis is not a primary factor in the regulation of enzyme secretion.