Search PubMed⌕ Search

Biomedical subjects

F Hirata

Publications and source records attributed to F Hirata.

At least 163 records · Page 9Linked to original sources
PubMed1979

beta-Adrenergic receptor agonists increase phospholipid methylation, membrane fluidity, and beta-adrenergic receptor-adenylate cyclase coupling.

The beta-adrenergic agonist L-isoproterenol stimulated the enzymic synthesis of phosphatidyl-N-monomethylethanolamine and phosphatidylcholine in rat reticulocyte ghosts containing the methyl donor S-adenosyl-L-methionine. The stimulation was stereospecific, dose-dependent, and inhibited by the beta-adrenergic agonist propranolol. The addition of GTP inside the resealed ghosts shifted the dose-response of phospholipid methylation by L-isoproterenol to the left by 2 orders of magnitude. Direct stimulation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] with sodium fluoride or cholera toxin did not increase the methylation of phospholipids. At a concentration of S-adenosyl-L-methionine that stimulates synthesis of phosphatidyl-N-monomethylethanolamine, the activity of isoproterenol-sensitive adenylate cyclase was increased 2-fold without changes in the basal activity of adenylate cyclase and the number of beta-adrenergic receptors. The increase of phospholipid methylation by L-isoproterenol decreased membrane viscosity and increased translocation of methylated lipids. These findings indicate that enhancement of phospholipid methylation by L-isoproterenol decreases membrane microviscosity and thus increases lateral movement of the beta-adrenergic receptors and coupling with adenylate cyclase.

Adenylyl Cyclases↗
PubMed1979

Concanavalin A stimulates phospholipid methylation and phosphatidylserine decarboxylation in rat mast cells.

When histamine release from rat peritoneal mast cells is stimulated by concanavalin A, membrane phospholipids are methylated in the early stage of this process. Exogenously added phosphatidylserine enhances the concanavalin A-induced histamine release, and at the same time the lectin markedly stimulates the decarboxylation and methylation of phosphatidylserine. Within minutes after the addition of concanavalin A to rat mast cells, the newly methylated phospholipids begin to disappear and an increased formation of lysophosphatidylcholine is observed. When rat mast cells are treated with concanavalin A in the absence of Ca2+, phospholipid methylation is stimulated but no significant release of histamine is detected. The subsequent exposure of the pretreated cells to Ca2+ causes increased release of histamine and degradation of methylated phospholipids. The inhibition of either synthesis or degradation of methylated phospholipids results in the inhibition of histamine release. These observations suggest that the synthesis and degradation of methylated lipids are an intrinsic part of the biochemical mechanism that modulate histamine release from mast cells.

Animals↗
PubMed1979

Formation of 5-hydroxykynurenine and 5-hydroxykynurenamine from 5-hydroxytryptophan in rabbit small intestine.

In order to clarify the role of indoleamine 2,3-dioxygenase [indole:oxygen 2,3-oxidoreductase (decyclizing), EC 1.13.11.17] in the metabolism of serotonin, DL-5-hydroxy[methylene-(14)C]tryptophan, a precursor of serotonin, was incubated with slices of rabbit ileum. Resulting metabolites were separated by DEAE-cellulose column and polyamide column chromatography and identified by various chromatographic techniques and enzymatic analysis. Metabolites obtained in significant amounts were serotonin, 5-hydroxyindoleacetic acid, 5-hydroxytryptophol, 5-hydroxykynurenine, 5-hydroxykynurenamine, and 4,6-dihydroxyquinoline, representing 13.2, 15.8, 7.0, 21.9, 1.3, and 2.6% of the total metabolites, respectively. The first three compounds were previously reported to be major metabolites produced from 5-hydroxytryptophan by the action of aromatic L-amino acid decarboxylase and monoamine oxidase, whereas the last three are formed by the cleavage of the indole ring by the action of indoleamine 2,3-dioxygenase. In the presence of pargyline, a monoamine oxidase inhibitor, the major metabolites obtained were serotonin, 5-hydroxykynurenine, and 5-hydroxykynurenamine, representing 29.6, 26.6, and 5.4% of the total metabolites, respectively. In the presence of RO4-4602, an aromatic amino acid decarboxylase inhibitor, 5-hydroxykynurenine was the sole major product. These results strongly suggest that the newly discovered metabolic pathway involving the cleavage of the indole ring of 5-hydroxytryptophan operates in vivo to a significant extent and that indoleamine 2,3-dioxygenase plays an important role in the regulation of serotonin levels in the small intestine of the rabbit.

5-Hydroxytryptophan↗
PubMed1979

Chemoattractants stimulate degradation of methylated phospholipids and release of arachidonic acid in rabbit leukocytes.

When rabbit peritoneal leukocytes were treated with chemoattractants such as fMet-Leu-Phe, an apparent decrease of [3H]methyl incorporation into the lipid fraction from L-[methyl-3H]methionine was observed. This decrease was a result of increased degradation of methylated phospholipids, not of decreased synthesis. Chemotactic peptides did not affect the metabolism of the phospholipids in which [methyl-14C]choline was incorporated. The disappearance of the [3H]methyl group was associated with the release of [1-14C]arachidonic acid from phospholipids prelabeled with these compounds. These findings suggested the activation by chemoattractants of phospholipase A2, an enzyme that removes an unsaturated fatty acid from phospholipids. The order of potency of chemoattractants for the stimulated degradation of phospholipids was in good agreement with that for chemotaxis. Mepacrine (quinacrine) and hydrocortisone inhibited and a phorbol ester enhanced both chemotaxis and phospholipase A2 activity. These results, taken together, suggest close association of the metabolism of methylated phospholipids with chemotaxis in rabbit peritoneal leukocytes.

Animals↗
PubMed1978

Indoleamine 2,3-dioxygenase. Formation of L-kynurenine from L-tryptophan in cultured rabbit fineal gland.

The distribution of the indoleamine 2,3-dioxygenase activity was investigated in various parts of the rabbit brain using the supernatant fraction (30,000 X g, 30 min) of homogenates. A low but significant activity was detected in all parts of the brain. The highest activity was associated with the pineal gland and choroid plexus. Specific activities of the supernatant fractions derived from the pineal gland and choroid plexus were 84.8 and 34.2 pmol/h/mg of protein at 37 degrees C, respectively, with L-tryptophan as substrate. When the pineal gland was cultured with L-[methylene-14C]tryptophan, L-[methylene-14C]kynurenine formed by the action of indoleamine 2,3-dioxygenase was found as one of the major products. It was isolated by DEAE-cellulose column chromatography and identified by thin layer chromatography with and without the treatment by kynureninase from a pseudomonad. The amount of kynurenine thus measured accounted for approximately one-third of the total amount of tryptophan metabolites, indicating that the kynurenine pathway is one of the major metabolic pathways of tryptophan in the rabbit pineal gland.

Animals↗
PubMed1978

Indoleamine 2,3-dioxygenase. Purification and some properties.

Indoleamine 2,3-dioxygenase was purified from rabbit small intestine to apparent homogeneity as judged by polyacrylamide gel electrophoresis and analytical ultracentrifugation. The native enzyme was a monomeric protein of a molecular weight of 41,000 +/- 1,000 with an s020,w value of 3.45 S. It had a relative abundance of hydrophobic amino acids such as valine, leucine, and isoleucine, and contained approximately 5% carbohydrate by weight. The estimated content of sugar residues per mol of enzyme was: galactose, 1.2; mannose, 2.6; N-acetylglucosamine, 5.2; and sialic acid, 0.8. One mole of enzyme had 0.8 mol of protoheme IX as a prosthetic group. However, copper was not detected in a significant amount and the ratio of copper to heme was less than 0.03. EPR spectra of the nitric oxide complex of the ferrous enzyme indicated that a nitrogen atom, possibly in an imidazole group, might be coordinated as the fifth ligand of the heme coenzyme. The anisotropic g values were gx = 2.08, gy = 1.98, and gz = 2.01. A single enzyme protein catalyzed the oxygenative ring cleavage of D- and L-tryptophan, D- and L-5-hydroxytryptophan, tryptamine, and serotonin. In addition, the purified enzyme had a peroxidase activity with guaiacol and potassium iodide as hydrogen donors, but not a catalase activity.

Amino Acids↗
PubMed1978

Identification and properties of two methyltransferases in conversion of phosphatidylethanolamine to phosphatidylcholine.

Two methyltransferases involved in the methylation of phosphatidylethanolamine to form phosphatidylcholine were demonstrated in a microsomal fraction of bovine adrenal medulla. The first methyltransferase catalyzes the methylation of phosphatidylethanolamine to form phosphatidyl-N-monomethylethanolamine. This enzyme has an optimum pH of 6.5, a low Km for S-adenosyl-L-methionine (1.4 micron), and an absolute requirement for Mg2+. The second methyltransferase catalyzes the two successive methylations of phodphatidyl-N-monomethylethanolamine to phosphatidyl-N,N-dimethylethanolamine and phosphatidylcholine. In contrast to the first methyltransferase, it has an optimum pH of 10 and a high Km for S-adenosyl-L-methionine (0.1 mM) and does not require Mg2+.

Adrenal Medulla↗
PubMed1978

Enzymatic synthesis and rapid translocation of phosphatidylcholine by two methyltransferases in erythrocyte membranes.

The synthesis of phosphatidylcholine from phosphatidylethanolamine is carried out by two methyltransferases in erythrocyte membranes. The first enzyme uses phosphatidylethanolamine as a substrate, requires Mg2+, and has a high affinity for methyl donor, S-adenosyl-L-methionine. The second enzyme methylates phosphatidyl-N-monomethylethanolamine to phosphatidylcholine and has a low affinity for S-adenosyl-L-methionine. The first enzyme is localized on the cytoplasmic side of the membrane and the second enzyme faces the external surface. This asymmetric arrangement of the two enzymes across the membrane makes possible the stepwide methylation of phosphatidylethanolamine localized on the cytoplasmic side and facilitates the rapid transmembrane transfer of the final product, phosphatidylcholine, to the external surface of the membrane. A mechanism for an enzyme-mediated flip-flop of phospholipids from the cytoplasmic to the outer surface of erythrocyte membranes is described.

Animals↗
PubMed1978

Studies on 15-hydroxyprostaglandin dehydrogenase with various prostaglandin analogues.

The NAD+-linked 15-hydroxyprostaglandin dehydrogenase (PGDH) of swine lung was purified to a high specific activity by affinity chromatographies on prostaglandin (PG)-and NAD+-Sepharose. The affinities of the enzyme for various synthetic analogues of PGA, E, F, and I and their inhibitory effects on the enzymatic reaction were examined. The modification of the alkyl side chain of PG, particularly at C-15 or C-16, reduced the affinity of the enzyme for these PG analogues. Furthermore, 14-methyl-13,14-dihydro-PGE1 and 16-cyclopentyl-omega-trinor-15-epi-PGE2 were potent inhibitors of PGDH.

Animals↗