PubMed Health⌕ Search

Biomedical subjects

T Kimura

Publications and source records attributed to T Kimura.

At least 19 recordsLinked to original sources
PubMed2001

Regulation of thyroid cell proliferation by TSH and other factors: a critical evaluation of in vitro models.

TSH via cAMP, and various growth factors, in cooperation with insulin or IGF-I stimulate cell cycle progression and proliferation in various thyrocyte culture systems, including rat thyroid cell lines (FRTL-5, WRT, PC Cl3) and primary cultures of rat, dog, sheep and human thyroid. The available data on cell signaling cascades, cell cycle kinetics, and cell cycle-regulatory proteins are thoroughly and critically reviewed in these experimental systems. In most FRTL-5 cells, TSH (cAMP) merely acts as a priming/competence factor amplifying PI3K and MAPK pathway activation and DNA synthesis elicited by insulin/IGF-I. In WRT cells, TSH and insulin/IGF-I can independently activate Ras and PI3K pathways and DNA synthesis. In dog thyroid primary cultures, TSH (cAMP) does not activate Ras and PI3K, and cAMP must be continuously elevated by TSH to directly control the progression through G(1) phase. This effect is exerted, at least in part, via the cAMP-dependent activation of the required cyclin D3, itself synthesized in response to insulin/IGF-I. This and other discrepancies show that the mechanistic logics of cell cycle stimulation by cAMP profoundly diverge in these different in vitro models of the same cell. Therefore, although these different thyrocyte systems constitute interesting models of the wide diversity of possible mechanisms of cAMP-dependent proliferation in various cell types, extrapolation of in vitro mechanistic data to TSH-dependent goitrogenesis in man can only be accepted in the cases where independent validation is provided.

Animals↗
PubMed1979

The formation of binary and ternary complexes of cytochrome P-450scc with adrenodoxin and adrenodoxin reductase.adrenodoxin complex. The implication in ACTH function.

Binary and ternary complexes of bovine adrenocortical mitochondrial cytochrome P-450scc with adrenodoxin and adrenodoxin reductase.adrenodoxin complex are formed in the presence of cholesterol and Emulgen 913. Both cholesterol and Emulgen 913 are required for the binding of cytochrome P-450scc with adrenodoxin. Since phospholipids are able to replace Emulgen 913 in this reaction, in vivo phospholipids of the mitochondrial inner membrane appear to play the function of the detergent. The dissociation constants of the cytochrome.adrenodoxin complex are 0.3 to 0.4 microM at 130 microM dimyristoylphosphatidylcholine and 0.9 microM at 120 microM Emulgen 913, whereas the dissociation constant for the ternary complex of cytochrome P-450scc with adrenodoxin reductase and adrenodoxin is 4.0 microM at 150 microM Emulgen 913. The stoichiometry of binary and ternary complexes reveals the 1:1 and 1:1:1 molar ratios, respectively, judging from chemical analyses after the fractionation of the complexes by gel filtration. Emulgen 913, Tween 20, ethylene glycol, myristoyllysophosphatidylcholine, dimyristoylphosphatidylcholine, and phosphatidylethanolamine show the enhanced activity of cholesterol side chain cleavage reaction with cytochrome P-450scc, adrenodoxin, adrenodoxin reductase, and NADPH. These results, in conjunction with earlier experiments, lead us to the proposal on the structure of the hydroxylase complex in the membrane and to the hypothesis on the regulation of the enzymatic activity by the availability of substrate cholesterol to the cytochrome. Hence, we propose a mobile P-450scc hypothesis for the response of the mitochondrion to adrenocorticotropic hormone stimuli.

Adrenal Cortex↗
PubMed1979

Topological studies of cytochromes P-450scc and P-45011 beta in bovine adrenocortical inner mitochondrial membranes. Effects of controlled tryptic digestion.

The topology of the steroid hydroxylase complexes in bovine adrenocortical mitochondria were studied by using controlled digestion with trypsin of purified inner mitochondrial membranes. Inhibition of steroid hydroxylase activity by trypsin was only observed in inner mitochondrial membranes which had been disrupted by various techniques. The steroid hydroxylase activity of intact inner membranes was not inhibited by trypsin. The effect of tryptic digestion was monitored by measuring 11 beta-hydroxylase and cholesterol side chain cleavage activities, as well as cytochrome P-450 reduction. The effect of trypsin on the steroid-induced difference spectra using pregnenolone, 20 alpha-hydroxycholesterol, and deoxycorticosterone was also measured. The results were similar regardless of which procedure was utilized and strongly suggest that both cytochrome P-45011 beta and cytochrome P-450scc are located on the matrix side of the mitochondrial inner membrane.

Adrenal Cortex↗
PubMed1979

Preparation and partial characterization of iron-sulfur, iron-selenium, and iron-tellurium complexes of bovine serum albumin.

An artificial Fe-S* protein was prepared by the reaction of bovine serum albumin with FeSO4 and Na2S or with a synthetic Fe-S*-1,4-butanenedithiol complex. These improved methods enabled us to characterize the derivatives from serum albumin. The Fe-S* albumin complex has about 20 iron ions and 14 labile sulfur atoms per molecule of the protein, whose absorption spectrum closely resembled that of 2Fe-2S* proteins. Its electron paramagnetic resonance spectrum exhibited signals different from those of ferredoxins. The addition of p-chloromercuriphenylsulfonate quenched the optical absorption in the visible region as well as the electron paramagnetic resonance signals. These properties of the albumin-iron complex are similar to those of iron-sulfur dithiothreitol and mercaptoethanol complexes, suggesting that the albumin-iron complex has one or more protein ligands besides sulfur lignads. Presumably, the oxygen atom of the tyrosine residue, or other hydroxyamino acids participates in the complex formation. In this context, the albumin polypeptide appears to be incapable of forming an iron-sulfur cluster identical to those of ferredoxins. Yet, from the albumin-iron derivative, the extrusion of the iron-sulfur core with benzenethiol provided products similar to those from ferredoxins. The iron-selenium and iron-tellurium derivatives of the bovine serum albumin were prepared and partially characterized by optical absorption and electron paramagnetic resonsnace spectroscopies. These results imply that both selenium and tellurium can be incorporated into the protein molecule as the respective labile components.

Chemical Phenomena↗
PubMed1979

Effect of diuresis on urokinase excretion rate.

UK excretion rate in the diuretic state was investigated in human and animal studies. Loading of water, beer or diuretics in man decreased the UK excretion rate as urine flow increased. A linear relation between UK excretion rate and urine specific gravity was observed. Simultaneous loading of water and exercise suppressed the decrease in UK excretion rate and the increase in urine flow. In animal studies, a null value for UK excretion rate was observed as a result of giving physiological saline and/or furosemide, and a remarkable increase in urine flow was induced. These results clearly suggest the existence of a relation between renal function and UK excretion rate.

Animals↗
PubMed1979

Solubility determination of barely aqueous-soluble organic solids.

Solubility determination of organic molecules having very low solubilities is hampered by such problems as slow equilibration during measurement, influence of impurities, and inherent heterogeneity in the energetic content of the crystalline solid. Three approaches to meeting these problems are presented. The first approach involves enhancing the dissolution rate by the addition of a water-immiscible solvent in which the organic solute is more soluble, thereby increasing the surface area available for dissolution. The second method is a combination of experimental data with a group contribution approach that allows the estimation of extremely insoluble solids. This approach involves measurement of the solubility in an organic solvent and calculation of the aqueous solubility from the estimated partition coefficient and the organic solvent data. The third approach is based on using a large excess of the solid and a highly specific analytical determination of the main component. The first two approaches were explored in detail and tested using norethindrone, norethindrone acetate, methyltestosterone, and methyltestosterone acetate.

Kinetics↗
PubMed1979

Clinical investigation of serum deoxyribonuclease: I. Analysis of serum deoxyribonuclease activity in comparison with normal and after endoscopic retrograde pancreatography.

Serum Deoxyribonuclease (DNase) micro-assay method was developed using 32P-labelled E. coli DNA as substrate. The serum DNase showed maximum activity at pH 7.5. It required Mg+ for activity, and was inhibited by EDTA or EGTA. The enzyme was also inhibited by actin (60-65%) or bovine pancreatic DNase I antibody (40-45%). The serum DNase activity was markedly increased following endoscopic retrograde pancreatography (ERP) examination. These results imply that serum DNase activity is mostly at least 60-65% pancreatic DNase I.

Actins↗
PubMed1979

Intrathymic injection of antigen: a potent procedure for the induction of suppressor T cells.

Immunological tolerance is induced in mice by intrathymic injection of HSA. The tolerance thus induced is mediated by suppressor T cells. Strong tolerance persists more than 56 days after the induction, and the high efficiency of the tolerance thus induced is accounted for in terms of the number or the potentiality of suppressor cells. Possible mechanisms of suppressor T cell induction by iT injection of the antigen are discussed briefly.

Animals↗