The topographical location and unique nature of a glucokinase associated with the Golgi apparatus of rat liver

Abstract

A particulate glucokinase was recovered in the Golgi-rich fraction of rat liver prepared by the method of Morre [Methods Enzymol. (1971) 22, 130-148], thus extending the demonstration by Berthillier et al. [Biochim. Biophys. Acta (1973) 293, 370-378] of particulate glucokinase activity in a microsomal subfraction that showed enrichment in Golgi characteristics. The purity of this fraction was examined and it was then subjected to several treatments, the action of Triton X-100, freezing and thawing, and sonication to establish the topographical location of the glucokinase activity thus solubilized. The evidence suggests that the glucokinase activity is either soluble in the lumen of the Golgi apparatus or loosely associated with the inside of the Golgi membranes. This Golgi glucokinase differs from the cytoplasmic enzyme in that it does not cross-react immunologically with an antiserum specific to the latter and in its binding to concanavalin ASepharose. The hepatic Golgi glucokinase is present in normal quantities in two situations, the livers of diabetic and neonatal rats, when the cytoplasmic enzyme activity is low or absent. A portion of the total hepatic activities of UTP-glucose 1-phosphate uridylyltransferase and phosphoglucomutase also appears to have a location in the Golgi apparatus. Together with the glucokinase these two enzymes would facilitate the biosynthesis of UDP-glucose, the donor in glucosylations, from glucose.

Immunohistochemical Evidence for the Presence of Glucokinase in the Gonadotropes and Thyrotropes of the Anterior Pituitary Gland of Rat and Monkey

“…A Golgi form of GK has previously been reported in the liver. That study also showed that the hepatic Golgi GK did not cross-react with an antiserum specific for cytoplasmic GK (Berthillier et al 1976).…”

Activities of glucokinase and hexokinase in mammalian and avian livers

“…(2) Liver extracts were always centrifuged at lOOOOOg for 60min before use of the supernatant for assay. This procedure should sediment particulate glucokinase activity (Berthillier et al, 1976) and also glucose-6-phosphatase (Hers et al, 1951). The latter can catalyse the phosphorylation of glucose with pyrophosphate as a phosphate donor (Nordlie & Lygre, 1966).…”

“…However, there are several differences between particulate and soluble glucokinase. Rat liver particulate glucokinase does not cross-react immunologically with an antiserum to soluble glucokinase, nor does its activity change in the livers of diabetic or neonatal rats, unlike the activity of soluble glucokinase (Berthillier et al, 1976). Furthermore, full particulate glucokinase activity is only obtained when liver extracts are sonicated or treated with detergents (Berthillier et al, 1976;Wals & Katz, 1981).…”

“…Rat liver particulate glucokinase does not cross-react immunologically with an antiserum to soluble glucokinase, nor does its activity change in the livers of diabetic or neonatal rats, unlike the activity of soluble glucokinase (Berthillier et al, 1976). Furthermore, full particulate glucokinase activity is only obtained when liver extracts are sonicated or treated with detergents (Berthillier et al, 1976;Wals & Katz, 1981). Since it has been shown that particulate glucokinase is involved in a pathway for the synthesis of UDP-glucose for glucosyltransferase reactions in the Golgi apparatus (Berthillier & Got, 1974), we have confined our studies to measurements of the activity of soluble glucokinase.…”

“…A particulate form of glucokinase has been found in rat liver (Berthillier et al, 1976) and the liver of two species of birds (Wals & Katz, 1981). However, there are several differences between particulate and soluble glucokinase.…”