Biosynthesis of Seminolipid : Sulfation in Vivo and in Vitro

Abstract

1. After a single injection of H₂⁵SO₄ intraperitoneally into a 6-week-old mouse, the radioactivity of testis seminolipid increased in the first day and decreased to half of the maximum level in one week. The highest incorporation rate was obtained around 10 days after birth. 2. Particulate fraction of boar testis was solubilized with Triton X-100. This enzyme preparation catalyzed the transfer of the sulfate group from PAPS ^** to desulfoseminolipid, yielding seminolipid. The reaction was stimulated by the addition of detergents and EDTA, and was inhibited by Mg²⁺ and ATP. The enzyme demonstrated a linear response for 30 min in the presence of desulfoseminolipid, and had an apparent K_m of 1.7×lO⁻³M. Desulfoseminolipid, galactosylceramide with hydroxy and non-hydroxy fatty acids and lactosylceramide were active as acceptors of sulfate from PAPS. Digalactosylceramide, trihexosylceramide, seminolipid, glucosylceramide, and cholesterol were not sulfated. Competition studies suggested that these glycolipids were sulfated by a single enzyme.