Composition and synthesis of gangliosides in mammary gland and milk of the bovine

Gangliosides of cultured cells of a rat mammary carcinoma cell line

Ganglioside content of rat mammary carcinoma-derived cells grown in layers in vitro was nearly as high as that of apical membrane-derived milk fat globule membrane and nearly four time higher than the content of normal, lactating mammary tissue on a protein basis. The major ganglioside of these carcinoma-derived cells was identified as GDla (sialic acid-Gal-GalNAc-sialic acid)-Gal-Glc-Cer. Relative to carcinoma-derived cells, rat mammary tissue and milk fat globule membrane had more complex ganglioside patterns but appeared to lack substantial quantities of GDla.

Composition and synthesis of three higher ganglioside homologs in bovine mammary tissue

Three higher gangliosides were identified as constituents of bovine mammary gland. The structures of these three gangliosides were shown to be ceramide-glucose-galactose-(sialic acid)-N-acetylgalactosamine-galactose, ceramide-glucose-galactose-(sialic acid)2-N-acetylgalactosamine, and ceramide-glucose-galactose-(sialic acid)2-N-acetylgalactosamine-galactose. These gangliosides accounted for only a small fraction (less than 20%) of the lipid-bound sialic in mammary gland. White fatty acids with even carbon numbers from C14 to C26 were predominant in these gangliosides, they also contained C23 and C25 fatty acids. Mammary gland Golgi apparatus-rich fractions had all glycosyltransferases required for synthesis of these gangliosides starting with ceramide.

Ganglioside biosynthesis. Characterization of CMP-N-acetylneuraminic acid : lactosylceramide sialyltransferase in Golgi apparatus from rat liver

An enzyme that transfers sialic acid from GMP-sialic acid to lactosylceramide was concentrated 40-50 times in Golgi apparatus from rat liver relative to total homogenates. This enzyme required detergents as dispersing agents. Of the numerous detergents tested, the combination Tween 80-Triton CF-54 (1 : 2, w/w) was the most effective in stimulating the reaction. Two apparent pH optima, at 6.35 and 5.5, were observed. The enzyme showed no requirement for a divalent cation. The Km values calculated for CMP-N-acetylneuraminic acid and lactosylceramide were 2.7 - 10(-3) and 1.3 - 10(-4) M, respectively. The enzyme could not be dissociated from Golgi apparatus fractions by treatment with ultrasound, indicating that it is tightly associated with the membrane. The newly synthesized GM3, the product of the reaction, was incorporated into or became tightly associated with the membranes of the Golgi apparatus.

Localization of some glycolipid glycosylating enzymes in the Golgi apparatus of rat kidney

Cell fractions from rat kidney were isolated and studied for their ability to synthesize several possible intermediates in the biosynthesis of sulfatides and gangliosides. The enzymes studied include UDP-Gal:ceramide galactosyltransferase, UDP-Gal:glucosylceramide galactosyltransferase, UDP-Gal:galactosylceramide galactosyltransferase, and CMP-NAN:lactosylceramide sialytransferase activities. The initial glycosylation of ceramide was found to be present in all of the kidney cell fractions studied. The remaining glycosylating enzymes were largely localized in the Golgi apparatus of kidney. Thus, in addition to modifying glycoproteins for secretion, the Golgi apparatus in kidney is involved in the modification of a number of glycolipids which are destined to form cell membrane components.

Biosynthesis and function of gangliosides

Gangliosides are unique acidic glycolipids that are selectively concentrated in the plasma membrane of cells. Surface labeling studies have demonstrated that at least a portion of the oligosaccharde chain of gangliosides extends beyond the hydrophe) is imbedded in the membrane bilayer. It is becoming increasingly apparent that gangliosides participate in the internalization of environmental signals elicited by cholera toxin and glycoprotein hormones such as thyrotropic hormone and chorionic gonadotropin as well as other substances such as interferon and possibly serotonin. The mechanism by which cholera toxin binds to a specific ganglioside receptor on the celraction of trophic agents with gangliosides. We would predict that analyogous phenomena involving gangliosides will be discovered in brain. The biosynthesis of gangliosides proceeds by the ordered sequential addition of sugars to the lipid moiety. These reactions are catalyzed by a cluster of membrane-bound glycosyltransferases. Any alteration in the activity or specificity of one of these enzymes will result in a dramatic change in the ganglioside pattern of an afflicted cell or organ. The drastic consequences that accompany abnormalities of ganglioside synthesis have been documented in a heritable metabolic disorder in vivo and in tumorigenic transformation of cells in vitro. In this article, we have attempted to unify these observations and to provide a reasonable interpretation of the role of gangliosides in mediating cell surface phenomena.

Neuronal-visceral GM1 gangliosidosis in a dog with beta-galactosidase deficiency

A 9-month-old dog with a history of progressive motor dysfunction was shown to have a deficiency in brain beta-galactosidase activity. The canine disease, like that of children with GM1 gangliosidosis, is characterized by accumulation of GM1 ganglioside in the brain, liver, and spleen, and membranous cytoplasmic bodies in neurons. The dog's pedigree suggests an autosomal recessive pattern of inheritance.