Effect of nucleotides on UDP-N-acetylglucosamine pyrophosphatase and N-acetylglucosaminyltransferase activities in microsomal membranes

1979 ◽  
Vol 57 (6) ◽  
pp. 557-565 ◽  
Author(s):  
Sailen Mookerjea
Keyword(s):  
Rat Liver ◽  
Liver Microsomes ◽  
Inhibitory Effect ◽  
Rat Liver Microsomes ◽  
Glycoprotein Synthesis ◽  
Microsomal Membranes ◽  
Pyrophosphatase Activity ◽  
Triton X ◽  
Hydrolysis Of

Rat liver microsomes solubilized by incubating with lysolecithin or Triton X-100 showed very active UDP-N-acetylglucosamine pyrophosphatase activity leading to the hydrolysis of the substrate into N-acetylglucosamine-1-P and N-acetylglucosamine. ATP, GTP, CDPcholine, and CDPglucose exerted a considerable inhibitory effect on the solubilized membrane pyrophosphatase activity. CDPcholine and CDPglucose, in addition, appeared to stimulate the transfer of N-acetylglucosamine into endogenous and exogenous acceptor proteins. Evidence is also presented of an inhibitory effect of ATP (and to some extent GTP) on N-acetylglucosaminyltransferase activity. This inhibitory effect of ATP and GTP became clearly evident when the pyrophosphatase activity in the membranes was virtually eliminated in the presence of CDPcholine and CDPglucose. The effect of ATP and GTP on the solubilized membrane enzymes indicated that the inhibition of pyrophosphatase activity alone did not determine the rate of transfer of sugar to protein. The results also suggested that the UDP-N-acetylglucosamine pyrophosphatase and N-acetyiglucosaminyltransferase activities were controlled independently and the effect of each nucleotide on these enzymes should, therefore, be carefully evaluated to understand its role in glycopolymer biosynthesis. Also, a possible role of choline and its derivatives in glycoprotein synthesis is discussed.

scholarly journals Characterization of the interaction between p100, a novel G-protein-related protein, and rat liver endosomes

1991 ◽  
Vol 280 (1) ◽  
pp. 171-178 ◽  
Author(s):  
L M Traub ◽  
E Shai ◽  
R Sagi-Eisenberg
Keyword(s):  
Rat Liver ◽  
Liver Microsomes ◽  
Rat Liver Microsomes ◽  
Trypsin Treatment ◽  
Putative Receptor ◽  
Microsomal Membranes ◽  
Direct Binding ◽  
Triton X ◽  
Binding Sequence

p100 is a recently identified 100 kDa protein which shares a putative receptor-binding sequence with the signal transducing G-proteins Gt and Gi. In liver, p100 immunoreactivity is distributed between the cytosolic and the microsomal fractions [Traub, Evans & Sagi-Eisenberg (1990) Biochem. J. 272, 453-458; Udrisar & Rodbell (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 6321-6325]. More specifically, we have localized the membrane-associated form of p100 to an endosomal subfraction of rat liver microsomes. In this study we have investigated the nature of the interaction between p100 and microsomal membranes. p100 was located on the cytoplasmic surface of the microsomal vesicles, and could be released by treatment with 0.5 M-NaCl or 0.5 M-Tris/HCl, pH 7.0. However, p100 was not released by non-ionic detergents, such as Triton X-100. Binding of p100 to the membrane was reversible, as both membrane-released and cytosolic p100 could re-bind stripped (Tris-washed) microsomes. Soluble p100 could not, however, bind to untreated microsomes. Binding to stripped microsomes approached saturation and was inhibited by up to 60% by either heat treatment or mild trypsin treatment of the vesicles. This implies that the interaction between p100 and the microsomal vesicles involves the direct binding of p100 to vesicular proteins. This binding was regulated by both adenine and guanine nucleotides. As p100 contains a region similar to the C-terminal decapeptide of alpha i, (the alpha-subunit of Gi) and has a localization that is restricted to an endosomal subfraction, we propose that cytosolic p100 may bind to cytoplasmically exposed domains of internalized receptors. Thus, like the adaptins, p100 may be involved in the process of sorting and receptor trafficking through the endosomal compartment of the cells.

scholarly journals A STUDY OF THE NUCLEOSIDE TRI- AND DIPHOSPHATE ACTIVITIES OF RAT LIVER MICROSOMES

1962 ◽  
Vol 15 (3) ◽  
pp. 563-578 ◽  
Author(s):  
Lars Ernster ◽  
Lois C. Jones
Keyword(s):  
Rat Liver ◽  
Liver Microsomes ◽  
Physiological Role ◽  
Sodium Deoxycholate ◽  
Inorganic Pyrophosphatase ◽  
Rat Liver Microsomes ◽  
High Concentrations ◽  
Hydrolysis Of ◽  
No Activation

Rat liver microsomes catalyze the hydrolysis of the triphosphates of adenosine, guanosine, uridine, cytidine, and inosine into the corresponding diphosphates and inorganic orthophosphate. The activities are stimulated by Na2S2O4, and inhibited by atebrin, chlorpromazine, sodium azide, and deaminothyroxine. Sodium deoxycholate inhibits the ATPase activity in a progressive manner; the release of orthophosphate from GTP and UTP is stimulated by low, and inhibited by high, concentrations of deoxycholate, and that from CTP and ITP is unaffected by low, and inhibited by high, concentrations of deoxycholate. Subfractionation of microsomes with deoxycholate into ribosomal, membrane, and soluble fractions reveals a concentration of the triphosphatase activity in the membrane fraction. Rat liver microsomes also catalyze the hydrolysis of the diphosphates of the above nucleosides into the corresponding monophosphates and inorganic orthophosphate. Deoxycholate strongly enhances the GDPase, UDPase, and IDPase activities while causing no activation or even inhibition of the ADPase and CDPase activities. The diphosphatase is unaffected by Na2S2O4 and is inhibited by azide and deaminothyroxine but not by atebrin or chlorpromazine. Upon fractionation of the microsomes with deoxycholate, a large part of the GDPase, UDPase, and IDPase activities is recovered in the soluble fraction. Mechanical disruption of the microsomes with an Ultra Turrax Blender both activates and releases the GDPase, UDPase, and IDPase activities, and the former effect occurs more readily than the latter. The GDPase, UDPase, and IDPase activities of the rat liver cell reside almost exclusively in the microsomal fraction, as revealed by comparative assays of the mitochondrial, microsomal, and final supernatant fractions of the homogenate. The microsomes exhibit relatively low nucleoside monophosphatase and inorganic pyrophosphatase activities, and these are unaffected by deoxycholate or mechanical treatment. Different approaches toward the function of the liver microsomal nucleoside tri- and diphosphatases are reported, and the possible physiological role of the two enzymes is discussed.

Autoregulation of 3, 3′,5′-triiodothyronine production by rat liver microsomes

1981 ◽  
Vol 98 (2) ◽  
pp. 240-245 ◽  
Author(s):  
T. Kaminski ◽  
J. Köhrle ◽  
R. Ködding ◽  
R.-D. Hesch
Keyword(s):  
Rat Liver ◽  
Incubation Medium ◽  
Liver Microsomes ◽  
Inhibitory Effect ◽  
Incubation Mixture ◽  
Rat Liver Microsomes ◽  
Experimental Conditions ◽  
Physiological Concentration ◽  
Enzyme Binding ◽  
Ph Dependent

Abstract. Conversion of thyroxine (T4) to 3,3′,5′-triiodothyronine (rT3) was studied in rat liver microsomes. Addition of rT3 at a physiological concentration to the incubation medium inhibited the deiodination of thyroxine to rT3. With a concentration of rT3 greater than 37.6 nM no net rT3 production at pH 8.0 was observed. Further increases in rT3 concentration resulted only in degradation of added rT3 and no net synthesis of rT3 from T4 could be detected. The inhibitory effect of rT3 upon its own production from T4 was pH dependent, 5 fold lower amounts of hormone being required to inhibit completely rT3 production at pH 7.4 than at pH 8.0. With the same experimental conditions no significant effect of rT3 on the conversion of T4 to 3,5,3′-triiodothyronine (T3) could be observed at pH 8.0 with all concentrations of added iodothyronine. A linear production of 3,3′-T2 from added rT3 was determined over the whole range of rT3 concentration, suggesting a lack of saturation of deiodinating enzyme. Binding of rT3 by anti-rT3 antibody added to the incubation mixture enhanced rT3 production from T4 by protecting rT3 from being degraded and/or diminishing the inhibitory effect of this iodothyronine on its own production. It was concluded that rT3 influenced its own production and that this effect may represent an important autoregulatory process in the iodothyronine metabolism.

Inhibitory Effect of Resveratrol on the Pharmacokinetics of Ticagrelor in Vivo and Vitro

2021 ◽  
Author(s):  
Peng Wang ◽  
Xiao-Xia Hu ◽  
Ying-hui Li ◽  
Nan-Yong Gao ◽  
Guo-quan Chen ◽  
...  
Keyword(s):  
Rat Liver ◽  
Liver Microsomes ◽  
In Vitro Study ◽  
Inhibitory Effect ◽  
Control Group ◽  
Rat Liver Microsomes ◽  
Sprague Dawley ◽  
Group B

This study was to evaluate the effect of resveratrol on the pharmacokinetics of ticagrelor in rats and the metabolism of ticagrelor in human CYP3A4 and liver microsomes. Eighteen Sprague-Dawley rats were randomly divided into three groups: group A (control group), group B (50mg/kg resveratrol), and group C (150mg/kg resveratrol ). After 30 minutes administration of resveratrol, a single dose of ticagrelor (18mg/kg) was administered orally. The vitro experiment was performed to examine the influence of resveratrol on ticagrelor metabolism in CYP3A4*1, human, and rat liver microsomes. Serial biological samples were assayed by validated UHPLC-MS/MS methods. In vivo study, the AUC and Cmax of ticagrelor in group B and C appeared to be significantly higher than the control group, while Vz/F and CLz/F of ticagrelor in group B and C were significantly decreased. In vitro study, resveratrol exhibited an inhibitory effect on CYP3A4*1, human and rat liver microsomes. The IC50 values of resveratrol were 56.75μM，69.07μM and 14.22μM, respectively. Our results indicated that resveratrol had a inhibitory effect on the metabolism of ticagrelor in vitro and vivo. It should be paid more attention to the clinical combination of resveratrol with ticagrelor and ticagrelor plasma concentration should be monitored to avoid the occurrence of adverse reaction.

Inhibitory effect of curcumin on fatty acid desaturation inMortierella alpina 1S-4 and rat liver microsomes

Lipids ◽  
1992 ◽  
Vol 27 (7) ◽  
pp. 509-512 ◽  
Author(s):  
Sakayu Shimizu ◽  
Saeree Jareonkitmongkol ◽  
Hiroshi Kawashima ◽  
Kengo Akimoto ◽  
Hideaki Yamada
Keyword(s):  
Fatty Acid ◽  
Rat Liver ◽  
Liver Microsomes ◽  
Inhibitory Effect ◽  
Fatty Acid Desaturation ◽  
Rat Liver Microsomes

A Study on the Effect of Lysolecithin and Phospholipase A on Membrane-Bound Galactosyltransferase

1974 ◽  
Vol 52 (11) ◽  
pp. 1053-1066 ◽  
Author(s):  
Sailen Mookerjea ◽  
James W. M. Yung
Keyword(s):  
Liver Microsomes ◽  
Fatty Acyl ◽  
Phospholipase A ◽  
Synthetase Activity ◽  
Rat Liver Microsomes ◽  
Physiological Concentration ◽  
Activation Effect ◽  
Membrane Bound ◽  
Hydrolysis Of

Addition of lysolecithin caused very marked activation of UDP-galactose:glycoprotein galactosyltransferase in rat liver microsomes and in Golgi-rich membranes. Lysolecithin activated galactosyltransferase when the enzyme was assayed both with endogenous acceptor and with exogenous proteins or monosaccharides as acceptors. Lactose synthetase activity in presence of α-lactalbumin was also stimulated by lysolecithin. Lecithin, lysophosphatidylethanolamine, lysophosphatidic acid, and glycerophosphorylcholine did not activate the enzyme, suggesting that both fatty acyl and phosphorylcholine groups of the lysolecithin molecule are required for the observed activation. The degree of activation was about the same when myristoyl-, palmitoyl-, oleoyl-, or stearoyllysolecithin were tested. The activation by lysolecithin was observed well within the physiological concentration of the lipid in the liver cell. Saturating amounts of Triton masked the effect of lysolecithin.Brief preincubation with phospholipase A activated the enzyme and generated lysolecithin in the membranes. Triton and lysolecithin activated the enzyme without any lag time, whereas phospholipase A activation was dependent on preincubation and also on an alkaline pH favorable for the hydrolysis of phospholipid. EDTA blocked the activation effect of phospholipase A but had no effect on activation by lysolecithin. Albumin and cholesterol opposed the effects of lysolecithin and phospholipase A on the enzyme. Two successive incubations of the microsomes with lysolecithin caused considerable release of the enzyme into the soluble fraction. The role of lysolecithin in the activation of the enzyme is probably related to the solubilization of the membrane and consequent enhanced interaction of the enzyme with substrate. Lysolecithin also activated N-acetylglucosaminyl- and sialyltransferase activities in microsomes. A possible role of lysolecithin is indicated in the regulation of glycosylation reactions in mammalian system.

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