Polyamine biosynthesis in human fetal liver and brain.

Abstract

Extract: S-Adenosylmethionine decarboxylase specific activity in fetal (9.0–25.0 cm crown-rump length) human liver was 20-fold greater than in mature human liver, both in the absence of putrescine (63.1 ± 7.2 versus 3.5 ± 0.8 pmol CO2/mg protein/30 min) or in the presence of putrescine (116.9 ± 8.2 versus 6.2 ± 1.0 pmol CO2/mg protein/30 min). Extracts of fetal human brain did not have a significantly greater specific activity of S-adenosylmethionine decarboxylase than extracts of mature human brain when assayed in the absence of putrescine and had less when assayed in the presence of putrescine (84.7 ± 14.9 versus 175.5 ± 30.6 pmol CO2/mg protein/30 min). Ornithine decarboxylase specific activity was greater in fetal liver than in mature liver (8.8 ± 1.6 versus 1.1 ±0.3 pmol CO2/mg protein/30 min) and 20-fold greater in fetal brain than in mature brain (71.2 ± 12.1 versus 3.1 ± 1.4 pmol CO2/mg protein/30 min). The concentration of putrescine was threefold greater in fetal human liver than in mature human liver (21.6 ± 2.7 versus 6.5 ± 0.5 μmol/100 g) and eightfold greater in fetal human brain than in mature human brain (42.9 ± 2.3 versus 5.5 ± 0.6 μmol/100 g). The concentration of spermidine was fourfold greater in fetal human liver than in mature human liver (81.2 ±1.6 versus 21.4 ± 1.2 μmol/100 g), but its concentration in fetal human brain was not different from that in mature human brain. Spermine concentration was greater in fetal human liver than in mature human liver (107.3 ± 2.4 versus 70.7 ± 6.8 μmol/100 g) and greater in fetal human brain than in mature human brain (30.7 ±1.8 versus 22.1 ±0.9 μmol/100 g). Speculation: The pathway of methionine metabolism in human fetal liver and brain is adapted to conserve the sulfur of homocysteine by delayed development of the trans-sulfuration of homocysteine to cysteine. This adaptation may implement RNA synthesis, as well as protein synthesis and DNA synthesis.