Biography:

In the past Thomas A. Brasitus has collaborated on articles with Pradeep K. Dudeja and Rajvir Dahiya. One of their most recent publications is CommunicationAlterations in the physical state and composition of brush border membrane lipids of rat enterocytes during differentiation. Which was published in journal Archives of Biochemistry and Biophysics.

More information about Thomas A. Brasitus research including statistics on their citations can be found on their Copernicus Academic profile page.

Thomas A. Brasitus's Articles: (29)

CommunicationAlterations in the physical state and composition of brush border membrane lipids of rat enterocytes during differentiation

AbstractThe physical state of the membrane lipid of brush border membranes, prepared from rat small intestinal villus and crypt cells, was examined by steady-state fluorescence polarization using three lipid-soluble fluorophors. Membranes prepared from crypt cells were found to possess a higher lipid fluidity than those of villus cells with each probe. Analysis of the composition of these membranes revealed that those from crypt cells had lower ratios of cholesterol/phospholipid (mol/mol), protein/lipid (ww), and saturated fatty acyl chains/unsaturated chains (ww). Alterations in the levels of stearic (18:0) and oleic (18:1) acids were responsible for differences in the latter ratio. The results, therefore, demonstrate that alterations in the lipid composition and fluidity of brush border membranes of enterocytes occur during the process of differentiation.

Regular paperLipid composition and fluidity of rat enterocyte basolateral membranes regional differences

AbstractThe lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.

Identification and partial characterization of phospholipid methylation in rat small-intestinal brush-border membranes

AbstractAn earlier study (Biochim. Biophys. Acta 46 (1961) 205–216) failed to detect the enzymatic synthesis of phosphatidylcholine (PC) from phosphatidylethanolamine (PE) via a transmethylation pathway in rat small-intestinal microsomal membranes. This pathway was therefore assumed to be absent from this organ. Recently, however, in our laboratory it has been demonstrated that this pathway for the synthesis of phosphatidylcholine is present in rat colonic brush-border and basolateral membranes. It was therefore of interest to examine whether phospholipid methylation activity was present in rat small-intestinal brush-border membranes. The results of the present experiments demonstrate for the first time that this pathway for the synthesis of phosphatidylcholine exists in these plasma membranes. Evidence to support the enzymatic nature of this reaction include: (1) loss of activity by heat denaturation and at 0°C, (2) significant inhibition by S-adenosyl-l-homocysteine and (3) saturation kinetics. The predominant product of this brush-border membrane phospholipid methyltransferase is phosphatidyl-N-monomethylethanolamine. This enzymatic activity has an apparent Km for S-adenosyl-l-methionine of 40 μM, a Vmax of 8.4 pmol/mg protein per 5 min, and a pH optimum of 8.0.

BBA reportEstrogen-induced alterations of the acidic and neutral glycosphingolipids of rat kidney

AbstractIn order to determine whether female sex hormones could influence the glycosphingolipid composition of the rat kidney, male albino rats of the Sherman strain were subcutaneously administered the synthetic estrogen, ethinylestradiol (5 mg/kg body wt. per day) or vehicle for 5 days, and the ganglioside, ceramide and neutral glycosphingolipid compositions of the kidneys of these animals were analyzed and compared. The results of these experiments demonstrate that estrogen treatment: (1) increased the ceramide, acidic and neutral glycosphingolipid contents of this tissue; (2) decreased the relative percentages of glucosyl- and globotetraosylceramide and hematoside (GM3), but increased the relative percentage of globotriaosylceramide and ‘other’ gangliosides; (3) increased the relative percentage of N-acetyl- to N-glycolylneuraminic acid in GM3; and (4) altered the long-chain bases of GM3, glucosyl- and globotetraosylceramide in this organ. These data, therefore, demonstrate that estrogen administration induces quantitative and qualitative alterations in the gangliosides, neutral glycosphingolipids and ceramide of the rat kidney. This data as well as a discussion of the possible physiological consequences of these estrogen-induced alterations in kidney glycosphingolipids serve as the basis for this report.

CommunicationAlterations in the physical state and composition of brush border membrane lipids of rat enterocytes during differentiation

AbstractThe physical state of the membrane lipid of brush border membranes, prepared from rat small intestinal villus and crypt cells, was examined by steady-state fluorescence polarization using three lipid-soluble fluorophors. Membranes prepared from crypt cells were found to possess a higher lipid fluidity than those of villus cells with each probe. Analysis of the composition of these membranes revealed that those from crypt cells had lower ratios of cholesterol/phospholipid (mol/mol), protein/lipid (ww), and saturated fatty acyl chains/unsaturated chains (ww). Alterations in the levels of stearic (18:0) and oleic (18:1) acids were responsible for differences in the latter ratio. The results, therefore, demonstrate that alterations in the lipid composition and fluidity of brush border membranes of enterocytes occur during the process of differentiation.

Regular paperLipid composition and fluidity of rat enterocyte basolateral membranes regional differences

AbstractThe lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.

Identification and partial characterization of phospholipid methylation in rat small-intestinal brush-border membranes

AbstractAn earlier study (Biochim. Biophys. Acta 46 (1961) 205–216) failed to detect the enzymatic synthesis of phosphatidylcholine (PC) from phosphatidylethanolamine (PE) via a transmethylation pathway in rat small-intestinal microsomal membranes. This pathway was therefore assumed to be absent from this organ. Recently, however, in our laboratory it has been demonstrated that this pathway for the synthesis of phosphatidylcholine is present in rat colonic brush-border and basolateral membranes. It was therefore of interest to examine whether phospholipid methylation activity was present in rat small-intestinal brush-border membranes. The results of the present experiments demonstrate for the first time that this pathway for the synthesis of phosphatidylcholine exists in these plasma membranes. Evidence to support the enzymatic nature of this reaction include: (1) loss of activity by heat denaturation and at 0°C, (2) significant inhibition by S-adenosyl-l-homocysteine and (3) saturation kinetics. The predominant product of this brush-border membrane phospholipid methyltransferase is phosphatidyl-N-monomethylethanolamine. This enzymatic activity has an apparent Km for S-adenosyl-l-methionine of 40 μM, a Vmax of 8.4 pmol/mg protein per 5 min, and a pH optimum of 8.0.

BBA reportEstrogen-induced alterations of the acidic and neutral glycosphingolipids of rat kidney

AbstractIn order to determine whether female sex hormones could influence the glycosphingolipid composition of the rat kidney, male albino rats of the Sherman strain were subcutaneously administered the synthetic estrogen, ethinylestradiol (5 mg/kg body wt. per day) or vehicle for 5 days, and the ganglioside, ceramide and neutral glycosphingolipid compositions of the kidneys of these animals were analyzed and compared. The results of these experiments demonstrate that estrogen treatment: (1) increased the ceramide, acidic and neutral glycosphingolipid contents of this tissue; (2) decreased the relative percentages of glucosyl- and globotetraosylceramide and hematoside (GM3), but increased the relative percentage of globotriaosylceramide and ‘other’ gangliosides; (3) increased the relative percentage of N-acetyl- to N-glycolylneuraminic acid in GM3; and (4) altered the long-chain bases of GM3, glucosyl- and globotetraosylceramide in this organ. These data, therefore, demonstrate that estrogen administration induces quantitative and qualitative alterations in the gangliosides, neutral glycosphingolipids and ceramide of the rat kidney. This data as well as a discussion of the possible physiological consequences of these estrogen-induced alterations in kidney glycosphingolipids serve as the basis for this report.

CommunicationAlterations in the physical state and composition of brush border membrane lipids of rat enterocytes during differentiation

AbstractThe physical state of the membrane lipid of brush border membranes, prepared from rat small intestinal villus and crypt cells, was examined by steady-state fluorescence polarization using three lipid-soluble fluorophors. Membranes prepared from crypt cells were found to possess a higher lipid fluidity than those of villus cells with each probe. Analysis of the composition of these membranes revealed that those from crypt cells had lower ratios of cholesterol/phospholipid (mol/mol), protein/lipid (ww), and saturated fatty acyl chains/unsaturated chains (ww). Alterations in the levels of stearic (18:0) and oleic (18:1) acids were responsible for differences in the latter ratio. The results, therefore, demonstrate that alterations in the lipid composition and fluidity of brush border membranes of enterocytes occur during the process of differentiation.

Regular paperLipid composition and fluidity of rat enterocyte basolateral membranes regional differences

AbstractThe lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.

Identification and partial characterization of phospholipid methylation in rat small-intestinal brush-border membranes

AbstractAn earlier study (Biochim. Biophys. Acta 46 (1961) 205–216) failed to detect the enzymatic synthesis of phosphatidylcholine (PC) from phosphatidylethanolamine (PE) via a transmethylation pathway in rat small-intestinal microsomal membranes. This pathway was therefore assumed to be absent from this organ. Recently, however, in our laboratory it has been demonstrated that this pathway for the synthesis of phosphatidylcholine is present in rat colonic brush-border and basolateral membranes. It was therefore of interest to examine whether phospholipid methylation activity was present in rat small-intestinal brush-border membranes. The results of the present experiments demonstrate for the first time that this pathway for the synthesis of phosphatidylcholine exists in these plasma membranes. Evidence to support the enzymatic nature of this reaction include: (1) loss of activity by heat denaturation and at 0°C, (2) significant inhibition by S-adenosyl-l-homocysteine and (3) saturation kinetics. The predominant product of this brush-border membrane phospholipid methyltransferase is phosphatidyl-N-monomethylethanolamine. This enzymatic activity has an apparent Km for S-adenosyl-l-methionine of 40 μM, a Vmax of 8.4 pmol/mg protein per 5 min, and a pH optimum of 8.0.

BBA reportEstrogen-induced alterations of the acidic and neutral glycosphingolipids of rat kidney

AbstractIn order to determine whether female sex hormones could influence the glycosphingolipid composition of the rat kidney, male albino rats of the Sherman strain were subcutaneously administered the synthetic estrogen, ethinylestradiol (5 mg/kg body wt. per day) or vehicle for 5 days, and the ganglioside, ceramide and neutral glycosphingolipid compositions of the kidneys of these animals were analyzed and compared. The results of these experiments demonstrate that estrogen treatment: (1) increased the ceramide, acidic and neutral glycosphingolipid contents of this tissue; (2) decreased the relative percentages of glucosyl- and globotetraosylceramide and hematoside (GM3), but increased the relative percentage of globotriaosylceramide and ‘other’ gangliosides; (3) increased the relative percentage of N-acetyl- to N-glycolylneuraminic acid in GM3; and (4) altered the long-chain bases of GM3, glucosyl- and globotetraosylceramide in this organ. These data, therefore, demonstrate that estrogen administration induces quantitative and qualitative alterations in the gangliosides, neutral glycosphingolipids and ceramide of the rat kidney. This data as well as a discussion of the possible physiological consequences of these estrogen-induced alterations in kidney glycosphingolipids serve as the basis for this report.

Rapid reportM3 muscarinic receptors on rat colonocytes are coupled to particulate guanylate cyclase activation

AbstractThe ability of muscarinic receptor antagonists to compete with (−)-[3H]quinuclidinyl benzilate ([3H]QNB) binding was compared with their ability to block carbachol-mediated stimulation of particulate guanylate cyclase activity in rat colonocytes. The binding of [3H]QNB to membranes was inhibited by antagonists with the following rank order of potencies (inhibitory constants, nM): atropine (2.5) ≈ 4-diphenylacetoxy-N-methylpiperidine iodide (4-DAMP) [4.6] ⪢ pirenzepine (121) >methoctramine (385). 4-DAMP (IC50 = ∼ 10 nM) was also more potent in blocking carbachol-induced stimulation of guanylate cyclase activity than either pirenzepine (IC50 = ∼ 700 nM) or methoctramine (IC50 = ∼ 1500 nM).

Rapid reportTPA causes divergent responses of Ca2+-dependent and Ca2+-independent isoforms of PKC in the nuclei of Caco-2 cells

AbstractThe present studies were undertaken to examine the expression of PKC isoforms within the nucleus of Caco-2 cells, a cell line widely used to investigate intestinal cell growth and differentiation, in order to begin to explore their roles in modulating gene expression. Purified nuclei were, therefore, prepared from Caco-2 cells and found to contain PKC-ζ, but not -α. The phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate (TPA) caused an acute redistribution of PKC-α to the nucleus, but did not change the distribution of PKC-ζ. Chronic treatment with TPA down-regulated total PKC-α, but not -ζ. Moreover, in contrast to acute TPA treatment, after chronic treatment, nuclear PKC-α was no longer detectable, whereas nuclear PKC-ζ was unchanged. These studies demonstrate for the first time the constitutive expression and divergent responses to TPA of the Ca2+-dependent and Ca2+-independent isoforms of PKC in the nuclei of Caco-2 cells and suggest that these specific isoforms may be involved in modulating gene expression.

BBA reportMembrane Lipids can modulate guanylate cyclase activity of rat intestinal microvillus membranes

AbstractStudies of the temperature dependence (10–40°C) of guanylate cyclase in rat intestinal microvillus membranes reveal a change in energy of activation (slope of the Arrhenius plot) at 30 ± 1°C. The break point temperature corresponds to the lipid thermotropic transition in these membranes previously characterized by differential scanning calorimetry (range: 23–39°C); peak temperature, 31°C). The break point temperature for guanylate cyclase also corresponds to that of a number of other microvillus membrane enzymes and of D-glucosem transport. These activities are defined as ‘intrinsic’ membrane brane activities by this operational criterion. Treatment with the nonionic detergent Lubrol WX increased the guanylate cyclase activity 4- to 8-fold and removed the discontinuity in the Arrhenius plot.

This month in Gastroenterology

AbstractGASTROENTEROLOGY 2000;119:287-288

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AbstractGASTROENTEROLOGY 2000;119:609-610

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AbstractGASTROENTEROLOGY 2000;119:889-890

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AbstractGASTROENTEROLOGY 1998;115:1311-1312

This month in Gastroenterology

AbstractGASTROENTEROLOGY 1998;115:1039-1040

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