Open AccessÉtude de l'activité de transfert de glucose, à partir d'UDP‐glucose, dans les membranes microsomiques des hépatocytes de rat
Author(s) -
BERTHILLIER Gisèle,
AZZAR Gérard J.C.,
GOT René
Publication year - 1975
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1975.tb03927.x
Subject(s) - chemistry , glycogen , biochemistry , membrane , glycogen branching enzyme , microsome , endogeny , enzyme , glycogen synthase , chromatography
Transfer of Glucose from UDP‐Glucose in Microsomal Membranes of Rat Hepatocytes Microsomal preparations from rat liver mediate transfer of glucosyl units from UDP‐glucose to three different kinds of acceptors: an endogenous glycoprotein, exogenous glycogen and collagen. Both glucosyl transferases work at acidic pH, 6.5 for transfer on endogenous acceptor and glycogen and at pH 5.5 for transfer on collagen. None of these enzymes require divalent cations for activity. While transfers on endogenous acceptor and glycogen are inhibited by the presence of a non‐ionic detergent, Triton X‐100, the transfer on collagen is activated by the same detergent. Glycogen‐synthase activity requires glucose 6‐phosphate at an optimal concentration of 1 mM. The K m values for UDP‐glucose are respectively: 0.5 mM, 0.33 mM, and 1 mM for transfer on endogenous acceptor, glycogen and collagen. Characterisation of the product indicates that a protein‐bound α1–4 glucan is formed when no primer is added. Enzymatic and acidic hydrolyses of radioactive glycogen and collagen show only glucose as a radioactive sugar identified by thin layer chromatography on cellulose. Pre‐treatment of microsomal membranes by α‐amylase demonstrates that glucosyltransferases are not adsorbed on endogenous glycogen and seem to be really membranous enzymes.