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 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 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 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 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 Lactose and fatty acid synthesis in lactating-rat mammary gland. Effects of starvation, re-feeding, and administration of insulin, adrenaline, streptozotocin and 2-bromo-α-ergocryptine

1984 ◽  
Vol 219 (1) ◽  
pp. 173-180 ◽  
Author(s):  
L E Bussmann ◽  
S Ward ◽  
N J Kuhn
Keyword(s):  
Mammary Gland ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Milk Composition ◽  
Standard Diet ◽  
Partial Recovery ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Intracellular Glucose

Lactose synthesis and fatty acid synthesis in intact lactating-rat mammary gland were measured simultaneously by incorporation of [U-14C]glucose and of both [U-14C]glucose and 3H2O respectively. Both processes were almost abolished by overnight starvation. Self-re-feeding caused recovery of lipogenesis to 100% of normal by 2 h and to 170% by 5 h. Lactose synthesis recovered to 80% of normal by 5 h. Food intubated to starved rats caused partial recovery in 3 h, standard diet favouring lactose synthesis and sugars favouring lipogenesis. Casein and starch were ineffective. Olive oil intubated to fed rats suppressed lipogenesis greatly and lactose synthesis slightly. Paraffin oil or water partly mimicked these effects. Adrenaline (subcutaneous) decreased lipogenesis from glucose, whereas insulin (subcutaneous) caused hypoglycaemia associated with loss of lactose synthesis but unchanged fatty acid synthesis. Streptozotocin and 2-bromo-alpha-ergocryptine (CB-154) impaired lipogenesis but not lactose synthesis. The results are interpreted in terms of competition for intracellular glucose by biosynthetic pathways for lactose and fat, and the possible implications for variations in milk composition are discussed.

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