Incorporation of [14C] glucosamine and [14C] leucine into mouse kidney beta-glucuronidase induced by gonadotrophin

Abstract

Male BALB/C mice were injected intraperitoneally with 2.5 i.u. of gonadotrophin. After the injection, increase of beta-glucuronidase activity was first observed in the microsomal fraction. By 36h 45-50% of the total homogenate activity was found in the microsomal fraction compared with 20-25% in the control microsomal fraction. From 36 to 80h not only microsomal beta-glucuronidase but also lysosomal beta-glucuronidase increased progressively. After 69h stimulation with 2.5 i.u. of gonadotrophin, d-[1-(14)C]glucosamine or l-[U-(14)C]leucine was injected intraperitoneally. After a further 3h the kidneys were homogenized and five particulate fractions were prepared by differential centrifugation. The beta-glucuronidase in the microsomal and lysosomal fractions was released respectively by ultrasonication and by freezing and thawing treatment. The enzyme was purified by organic-solvent precipitation and by sucrose-density-gradient centrifugation. The results demonstrated the incorporation of these two labels into the mouse renal beta-glucuronidase. The microsomal beta-glucuronidase was much more radioactive than the lysosomal enzyme and approx. 80% of the newly synthesized enzyme appeared in microsomes and approx. 20% of that was found in lysosomes at this period. These results suggest that the mouse renal beta-glucuronidase is a glycoprotein and that the newly synthesized enzyme is transported from endoplasmic reticulum to lysosomes.