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 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.

The role of insulin in the regulation of AMP-activated protein kinase in lactating rat mammary gland

1992 ◽  
Vol 20 (3) ◽  
pp. 306S-306S ◽  
Author(s):  
MIHAJLO R. MILIC ◽  
KAREN A. OTTEY ◽  
SARVJINDER TAKHAR ◽  
MICHAEL R. MUNDAY
Keyword(s):  
Mammary Gland ◽  
Protein Kinase ◽  
Rat Mammary Gland ◽  
Amp Activated Protein Kinase

scholarly journals Control of glucose metabolism in isolated acini of the lactating mamary gland of the rat. Effects of oleate on glucose utilization and lipogenesis

1978 ◽  
Vol 170 (3) ◽  
pp. 609-613 ◽  
Author(s):  
A M Robinson ◽  
D H Williamson
Keyword(s):  
Mammary Gland ◽  
Glucose Metabolism ◽  
Glucose Utilization ◽  
Substrate Utilization ◽  
Inhibitory Effects ◽  
Rat Mammary Gland

Oleate (1mM) had only small inhibitory effects on glucose utilization and lipogenesis in acini isolated from rat mammary gland. Esterification of [1-14C]oleate was unaffected by insulin but were decreased by 60% by acetoacetate (2mM). Glycerol (1mM), but not insulin, relieved this inhibition. These experiments provide further support for the role of acetoacetate in regulating substrate utilization by the gland.

Assessment of mammary gland metabolism in the sow: III. Cellular metabolites in the mammary secretion and plasma following weaning

1995 ◽  
Vol 62 (2) ◽  
pp. 221-236 ◽  
Author(s):  
Craig S. Atwood ◽  
Peter E. Hartmann
Keyword(s):  
Mammary Gland ◽  
Metabolic Activity ◽  
De Novo ◽  
Acid Synthesis ◽  
Mammary Glands ◽  
Rapid Decrease ◽  
Rapid Changes ◽  
Lactose Synthase ◽  
Lactogenic Hormones ◽  
Lactose Synthesis

SUMMARYThe concentrations of lactose, glucose, glucose 6-phosphate, glucose 1-phosphate, UDPglucose, UDPgalactose, UDP, UMP, inorganic phosphate, ADP and AMP (metabolites involved in the lactose synthesis pathway), and cAMP, galactose and sodium were measured in the mammary secretion from four or five mammary glands on each of six sows during the first 5 d post weaning. The concentrations of lactose, glucose and galactose were also measured in plasma during this time. Following weaning, the rapid increase in the concentrations of glucose 6-phosphate and UDPgalactose suggested that the rate of lactose synthesis was regulated by the inhibition of hexokinase and/or lactose synthase, while the decrease in glucose and AMP indicated a subsequent decline in glucose and ATP utilization. The rapid increase in glucose 6-phosphate which plays a pivotal role as a substrate for both lactose and de novo fatty acid synthesis, and the rapid decrease in AMP which reflects ATP utilization, were good markers of decreased metabolic activity. These rapid changes in the metabolic activity of the mammary glands were not observed in a second weaning study when two piglets were removed from selected mammary glands for periods up to 5 h during established lactation. Since concentrations of lactogenic hormones remain elevated following partial weaning, but fall following total weaning (Rojkittikhun et al. 1991), these differences in mammary gland metabolism indicate that endocrine rather than autocrine mechanisms are controlling lactose and fat synthesis during the initial stages of total weaning.

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 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.

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