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 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.

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 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 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 Composition, stability and electrolyte permeability of Golgi membranes from lactating-rat mammary gland

1981 ◽  
Vol 200 (3) ◽  
pp. 663-669 ◽  
Author(s):  
M D White ◽  
S Ward ◽  
N J Kuhn
Keyword(s):  
Mammary Gland ◽  
Membrane Lipids ◽  
Periodic Acid ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Membrane Vesicles ◽  
Periodic Acid Schiff ◽  
Wide Ph Range ◽  
Rat Mammary Gland ◽  
Ph Range

1. Golgi membrane vesicles, isolated from lactating-rat mammary gland and greatly enriched in galactosyltransferase (EC 2.4.1.22), contained over 40 separate bands of protein, including some periodic acid)(Schiff-staining material and free thiol groups, when analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 2. The membrane lipids were enriched in phosphatidylcholine, phosphatidylethanolamine and unesterified cholesterol. 3. Membrane fluidity, as monitored by the fluorescence polarization of 1,6-diphenylhexa-1,3,5-triene, increased linearly over 5-37 degrees C. 4. The vesicle membranes were impermeable to lactose over a wide pH range, but admitted electrolytes of molecular weight below about 300. 5. These properties are discussed with respect to other cellular membranes and the secretion of milk products.

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