Cystathionase: immunochemical evidence for absence from human fetal liver.

Abstract

Extract: Purified human liver cystathionase was obtained by ammonium sulfate fractionation (45–65% saturation), starch block electrophoresis, and disc gel electrophoresis. Antibodies to the human enzyme were induced in the rabbit using cystathionase in polyacrylamide disc gel as antigen. A pooled homogenate of liver from 14 human fetuses (5.7 to 20 cm crown-rump length), obtained at therapeutic abortion, was compared by agar double diffusion with an homogenate from normal human adult liver. A specific enzymatic stain, using cystathionine as substrate, was used to detect cystathionase activity in the immune precipitate. The extract of fetal liver did not form an enzymatically inactive immune precipitin band uniting with the catalytically active band formed between the adult liver and the antiserum. This absence was confirmed by immunotitration studies using a mixture of adult and fetal liver extracts in which the amount of fetal liver extract was equivalent to three times the total protein in the adult liver extract. The addition of fetal liver did not appreciably increase the amount of cystathionase activity remaining in the supernatant after combination with a given quantity of antibody and centrifugation to remove the enzyme-antibody complex. Speculation: Human fetal liver does not contain an enzymatically inactive precursor protein immunologically related to adult human liver cystathionase, giving evidence that the human fetus is not competent to synthesize more than trace amounts of the intact enzyme.