scholarly journals Evidence for specific transport of uridine diphosphate galactose across the Golgi membrane of rat mammary gland

1976 ◽  
Vol 154 (1) ◽  
pp. 243-244 ◽  
Author(s):  
N J Kuhn ◽  
A White
Keyword(s):  
Mammary Gland ◽  
Golgi Apparatus ◽  
Facilitated Transport ◽  
Uridine Diphosphate ◽  
Golgi Membrane ◽  
Specific Transport ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Uridine Diphosphate Galactose

The inhibition of lactose synthesis by UDP-glucose, UDP-glucuronate and, less so, by UDP-N-acetylglucosamine was markedly smaller in preparations of “intact” than of lysed vesicles derived from the Golgi apparatus of lactating rat mammary gland. This constitutes evidence for a specific, probably facilitated, transport of UDP-galactose across the Golgi membrane.

scholarly journals Mannitol and glucose movement across the Golgi membrane of lactating-rat mammary gland

1981 ◽  
Vol 194 (1) ◽  
pp. 173-177 ◽  
Author(s):  
M D White ◽  
N J Kuhn ◽  
S Ward
Keyword(s):  
Mammary Gland ◽  
Pore Size ◽  
Membrane Vesicles ◽  
Golgi Membrane ◽  
First Order ◽  
First Order Kinetics ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Kinetics Of ◽  
Uptake And Release

1. Purified Golgi-membrane vesicles of lactating-rat mammary gland were penetrated by glucose. 3-O-methylglucose, mannose, fructose, sorbitol and mannitol, but not by lactose or sucrose. 2. The kinetics of mannitol uptake and release were followed at 2-6 degrees C with the aid of fine filters (0.45 micrometers pore size) to separate the vesicles from the medium. 3. Mannitol efflux exhibited apparent first-order kinetics with k approximately 1 min-1. Neither saturability, nor inhibition by excess sorbitol or glucose, could be observed. 4. Mannitol efflux at 18 degrees C was about seven times faster than at 1 degrees C, and rates at higher temperatures were too fast to be measured. The rate of glucose efflux at 2-6 degrees C exceeded that of mannitol severalfold. 5. These findings imply a channel or carrier of definite, but limited, specificity straddling the Golgi membrane and able to supply glucose for lactose synthesis.

Lactose Synthesis by a Golgi Apparatus Fraction from Rat Mammary Gland

Nature ◽  
1970 ◽  
Vol 228 (5276) ◽  
pp. 1105-1106 ◽  
Author(s):  
T. W. KEENAN ◽  
D. JAMES MORRÉ ◽  
R. D. CHEETHAM
Keyword(s):  
Mammary Gland ◽  
Golgi Apparatus ◽  
Rat Mammary Gland ◽  
Lactose Synthesis

scholarly journals Permeability of lactating-rat mammary gland Golgi membranes to monosaccharides

1980 ◽  
Vol 190 (3) ◽  
pp. 621-624 ◽  
Author(s):  
M D White ◽  
N J Kuhn ◽  
S Ward
Keyword(s):  
Mammary Gland ◽  
Membrane Vesicles ◽  
Golgi Membrane ◽  
Temperature Dependent ◽  
Golgi Membranes ◽  
Rat Mammary Gland ◽  
Lactose Synthesis

The Golgi-membrane vesicles present in particulate preparations of lactating rat mammary gland were biosynthetically loaded with [14C]lactose. This lactose was effectively retained by particles sedimented after exposure to 0.25 M-disaccharide, but was partly lost after exposure to 0.25 M-glucose or other solutes of similar size. Loss of lactose was time-, concentration- and temperature-dependent and varied with the solute structure. This behaviour is ascribed to the presence of protein in the Golgi membrane, forming a specific carrier or channel that serves to supply glucose for lactose synthesis.

scholarly journals The topography of lactose synthesis

1975 ◽  
Vol 148 (1) ◽  
pp. 77-84 ◽  
Author(s):  
N J Kuhn ◽  
A White
Keyword(s):  
Mammary Gland ◽  
Transport System ◽  
Active Site ◽  
Golgi Membrane ◽  
Glucose Transport System ◽  
Lactose Synthase ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Relationship Of ◽  
The Relationship

1. At short incubation times, and under suitable osmotic conditions, the lactose synthesized by Golgi-derived vesicles of rat mammary gland is 85-90% particulate. Evidence is presented for its occlusion within the lumen of the vesicles. 2. Ovalbumin is used as a bulky active-site inhibitor to show that the active site of lactose synthase lies on the inner face of the Golgi membrane. 3. Phlorrhizin and phloretin inhibit lactose synthesis by such vesicles, indicating the presence of a glucose-transport system. 4. The relationship of this topography to the synthesis of N-acetylneuraminyl-lactose and to the secretion of milk sugars is discussed.

scholarly journals The role of nucleoside diphosphatase in a uridine nucleotide cycle associated with lactose synthesis in rat mammary-gland Golgi apparatus

1977 ◽  
Vol 168 (3) ◽  
pp. 423-433 ◽  
Author(s):  
N J Kuhn ◽  
A White
Keyword(s):  
Mammary Gland ◽  
Uridine Nucleotide ◽  
Lactose Synthase ◽  
Bivalent Metal Ions ◽  
Ump Kinase ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Galactose Utilization ◽  
Nucleoside Diphosphatase

1. UDP-galactose utilization by isolated Golgi vesicles or rat mammary gland synthesizing lactose causes accumulation of UMP but not UDP, although UDP is the immediate product of lactose synthase (EC 2.4.1.22). 2. This can be ascribed to a nucleoside diphosphatase (EC 3.6.1.6), specific for UDP, GDP and IDP, activated by bivalent metal ions and apparently located on the luminal face of the Golgi membrane. 3. The uridine diphosphatase activity exceeds the total galactosyltransferase activity 5-fold, and is estimated to maintain UDP at about 14 micrometer within the Golgi lumen. 4. Evidence is given that UMP, but not UDP, penetrates the membrane and that UMP is rephosphorylated to UDP by a UMP kinase located in the cytosol. 5. Golgi-cytosol relationships with respect to lactose synthesis are formulated in terms of a uridine nucleotide cycle which throws new light on the energy cost and possible regulation of lactose synthesis.

scholarly journals Effects of phlorrhizin and thiol reagents on the galactosyltransferase activity of Golgi membrane vesicles of lactating rat mammary gland

1980 ◽  
Vol 188 (2) ◽  
pp. 503-507 ◽  
Author(s):  
N J Kuhn ◽  
A White
Keyword(s):  
Mammary Gland ◽  
Membrane Vesicles ◽  
Golgi Membrane ◽  
No Inhibition ◽  
Glucose Analogues ◽  
Rat Mammary Gland

1. The ability of phlorrhizin to inhibit the galactosylation of glucose was re-examined with Golgi membrane vesicles purified from rat mammary gland, and extended to the galactosylation of several glucose analogues and N-acylglucosamines. 2. The inhibition is ascribed, contrary to previous conclusions, to a general annealing of leaky membranes comprising a minority of the vesicles. 3. Three thiol reagents were able to inhibit the galactosylation of N-acylglucosamines with less, or no, inhibition of galactosylation of glucose. This demonstrates the existence of a Golgi membrane carrier that distinguishes between glucose and N-acylglucosamines.

scholarly journals Mechanism of glycosylation in the Golgi apparatus.

1983 ◽  
Vol 31 (8) ◽  
pp. 1033-1040 ◽  
Author(s):  
B Fleischer
Keyword(s):  
Plasma Membrane ◽  
Golgi Apparatus ◽  
Serum Proteins ◽  
Membrane Vesicles ◽  
Uridine Diphosphate ◽  
Golgi Membrane ◽  
Membrane Glycoproteins ◽  
Plasma Membrane Vesicles ◽  
Golgi Vesicles

A major role of the Golgi apparatus in liver is the terminal glycosylation of secreted serum proteins and of plasma membrane glycoproteins. Galactosyltransferase is a membrane-bound Golgi enzyme that transfers galactose directly from uridine diphosphogalactose (UDP-Gal) to terminal N-acetylglucosamine groups of N-asparagine-linked glycoproteins during secretion. Sialytransferase then transfers sialic acid from cytidine monophosphosialic acid (CMP-NAN) to the newly added terminal galactose of the glycoprotein. In the cell, the transfer reaction must occur on the lumen side of the Golgi membrane. UDP-Gal is synthesized mainly in the cytoplasm and CMP-NAN is synthesized in the nucleus in liver. An important question for understanding the mechanism is, how do these nucleotide sugars gain access to the transferases? A second question involves uridine diphosphate (UDP), a highly inhibitory product of galactosyltransferase. How is UDP removed from the lumen of the Golgi fast enough to prevent product inhibition of the galactosyltransferase? We have shown that isolated Golgi, although vesiculated, retains its original orientation. The vesicles are oriented with greater than 90% of both galactosyltransferase and sialyl-transferase on the luminal side of the vesicles. Using intact vesicles, we can show that UDP-Gal is taken up via a saturable carrier system present in the Golgi membrane. During galactosylation in vitro, UDP formed in the lumen of Golgi vesicles is rapidly converted to UMP by a nucleoside diphosphatase in the lumen. Uridine monophosphate, which is much less inhibitory to the galactosyltransferase than UDP, is then transported out of the lumen by a second carrier and is broken down further to uridine by 5'-nucleotidase on the cytoplasmic side of the Golgi vesicles. The transport of nucleotides appears unique to the Golgi membranes, since neither rough endoplasmic reticulum nor plasma membrane vesicles from rat liver accumulate these nucleotides.

scholarly journals Lactogenesis in the rat. Metabolism of uridine diphosphate galactose by mammary gland

1968 ◽  
Vol 106 (3) ◽  
pp. 743-748 ◽  
Author(s):  
N. J. Kuhn
Keyword(s):  
Mammary Gland ◽  
Synthetase Activity ◽  
Uridine Diphosphate ◽  
Parallel Increase ◽  
Hydrolytic Activities ◽  
Before And After ◽  
Rat Mammary Gland ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Rate Limiting

1. Lactose synthetase activity in the rat mammary gland increases during the last day of pregnancy from an essentially zero value. There is a parallel increase of tissue lactose and of glucose 6-phosphate dehydrogenase activity. 2. Mammary-gland homogenates prepared both before and after parturition hydrolyse the lactose precursors glucose 6-phosphate, glucose 1-phosphate, UDP-glucose, UDP-galactose and also maltose, but not lactose. 3. A role of lactose synthetase as the rate-limiting enzyme for lactose biosynthesis and the possible significance of the hydrolytic activities are discussed with respect to lactogenesis.

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