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 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 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 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.

Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland

2006 ◽  
Vol 291 (5) ◽  
pp. E1059-E1066 ◽  
Author(s):  
Adriana López ◽  
Nimbe Torres ◽  
Victor Ortiz ◽  
Gabriela Alemán ◽  
Rogelio Hernández-Pando ◽  
...  
Keyword(s):  
Gene Expression ◽  
Amino Acids ◽  
Mammary Gland ◽  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Amino Acid Transport System ◽  
System A ◽  
Rat Mammary Gland

Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. β-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.

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 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 Building a model of a problem situation in transport systems

2022 ◽  
Vol 14 (2) ◽  
pp. 4-9
Author(s):  
Viktor Aulin ◽  
◽  
Dmitrо Golub ◽  
Viktor Bilichenko ◽  
Artem Zamurenko ◽  
...  
Keyword(s):  
Decision Making ◽  
Transport System ◽  
Block Diagram ◽  
A Priori ◽  
Transport Systems ◽  
Problem Situation ◽  
Efficiency Criterion ◽  
Relationship Of ◽  
The Relationship ◽  
Selection Of

The approach to construction of model of a problem situation in transport system is resulted, the block diagram of its algorithm is developed. It is revealed that the transition stage from the problem to the formulation of formal tasks is a problem situation, and the tasks can be solved in different ways, forming a set of strategies. It is noted that in the general case the result of operations is uncertain, which is caused by the uncertainty of the conditions of the operation and the action of factors of different nature. It is revealed that the acquisition of values of indicators that characterize one or another result of the operation is associated with the solution of the problem of modeling operations. The stages of the problem of studying the efficiency of the operation in the transport system are given. A number of assumptions are made about the process of obtaining results, which is associated with the formation of the operation model and obtaining efficiency estimates based on modeling results, as well as the process of analyzing the results, which involves solving the selection problem based on the established efficiency criterion or system of such criteria. It is found that the model of the problem situation in transport systems reflects the relationship of the main elements of the decision-making process and the sequence of formation of partial tasks and is built to cover the problem of decision-making as a whole, to present its main elements to be finalized. about the strategy of the operation. It is shown that the presence of a certain component as an independent element in the model of the problem situation assumes that the set of values of uncertain factors in the development of solutions will be either set externally, or finding these values will be an independent task. A list of actions for solving partial problems based on this model is presented. It is shown that in many practical cases it is observed that the a priori task of one of the main criteria of efficiency leads to the selection of some set of alternatives. Therefore, the choice of the best alternative requires the formation of a compound criterion, which includes both formal and informal prescriptions for making a judgment on the basis of which the selection or return and correction of elements of the model of the problem situation.

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