Premium
GT3 Synthesis in the Proximal Golgi Occurs in a Compartment Different from Those for GD3 and GM3 Synthesis
Author(s) -
Rosales Fritz Víctor M.,
Maxzúd Mariana K.,
Maccioni Hugo J. F.
Publication year - 1996
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1996.67041393.x
Subject(s) - lactosylceramide , golgi apparatus , monensin , glycolipid , ganglioside , biochemistry , golgi membrane , chemistry , biosynthesis , incubation , biology , endoplasmic reticulum , enzyme
Previous studies from this laboratory have shown that synthesis of GT3, the precursor of c series gangliosides, occurs in proximal Golgi compartments, as has been shown for the synthesis of GM3 and GD3, the precursors of a and b series gangliosides, respectively. In this work we studied whether the synthesis of GM3, GD3, and GT3 occurs in the same or in different compartments of the proximal Golgi. For this, we examined in retina cells (a) the effect of monensin, a sodium ionophore that affects mostly the trans Golgi and the trans Golgi network function, on the metabolic labeling of glycolipids from [ 3 H]Gal by cultured cells from 7‐ and 10‐day chick embryos and (b) the labeling in vitro of endogenous glycolipids of Golgi membrane preparations from 7‐day embryos incubated with UDP‐[ 3 H]Gal. In (a), 1 µ M monensin produced a twofold accumulation of radioactive glucosylceramide and a decrease to ∼50 and 20% of total ganglioside labeling in 7‐ and 10‐day cells, respectively. At both ages, monensin produced a threefold accumulation of radioactive GM3 and an inhibition of >90% of GT3, GM1, GD1a, and GT1b synthesis. GD3 synthesis was inhibited ∼30 and 70%, respectively, in 7‐ and 10‐day cells. In (b), >80% of the [ 3 H]Gal was incorporated into endogenous glucosylceramide to form radioactive lactosylceramide. About 90% of [ 3 H]Gal‐labeled lactosylceramide was converted into GM3, and most of this in turn into GD3 when unlabeled CMP‐NeuAc was also present in the incubation system. Under the same conditions, however, <5% of labeled GD3 was converted into GT3. Golgi membranes incubated with CMP‐[ 3 H]NeuAc incorporated ∼20% of [ 3 H]NeuAc into endogenous GT3, and this percentage was not affected by 1 µ M monensin. These results indicate that synthesis of GT3 is carried out in a compartment of the proximal Golgi different from those for lactosylceramide, GM3, and GD3 synthesis. Results from the experiments with monensin point to the cis/medial Golgi as the main compartment for coupled synthesis of lactosylceramide, GM3, and GD3 and to the trans Golgi as the main compartment for synthesis of GT3.