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Biomedical subjects

K Niki

Publications and source records attributed to K Niki.

At least 37 records · Page 2Linked to original sources
PubMed1991

1H NMR studies on ferricytochrome c3 from Desulfovibrio vulgaris Miyazaki F and its interaction with ferredoxin I.

The 1H NMR signals of the heme methyl, propionate and related chemical groups of cytochrome c3 from Desulfovibrio vulgaris Miyazaki F (D.v. MF) were site-specifically assigned by means of 1D NOE, 2D DQFCOSY and 2D TOCSY spectra. They were consistent with the site-specific assignments of the hemes with the highest and second-lowest redox potentials reported by Fan et al. (Biochemistry, 29 (1990) 2257-2263). The site-specific heme assignments were also supported by NOE between the methyl groups of these hemes and the side chain of Val18. All the results contradicted the heme assignments for D.v. MF cytochrome c3 made on the basis of electron spin resonance (Gayda et al. (1987) FEBS Lett., 217 57-61). Based on these assignments, the interaction of cytochrome c3 with D.v. MF ferredoxin I was investigated by NMR. The major interaction site of cytochrome c3 was identified as the heme with the highest redox potential, which is surrounded by the highest density of positive charges. The stoichiometry and association constant were two cytochrome c3 molecules per monomer of ferredoxin I and 10(8) M-2 (at 53 mM ionic strength and 25 degrees C), respectively.

Binding Sites↗
PubMed1990

Estimation of microscopic redox potentials of a tetraheme protein, cytochrome c3 of Desulfovibrio vulgaris, Miyazaki F, and partial assignments of heme groups.

The microscopic formal redox potentials of a tetraheme protein, cytochrome c3 from Desulfovibrio vulgaris, Miyazaki F, were estimated from the chemical shifts of the heme methyl signals in its 1H NMR spectrum. All chemical shifts in the five macroscopic oxidation states were determined for eight of the heme methyl protons by the saturation-transfer method. The electron-distribution probability at each heme in each oxidation state was estimated directly from the chemical shifts. To minimize errors due to interheme pseudocontact contributions, the average electron-distribution probability was used for calculation of the microscopic formal redox potentials. By introducing interacting potentials, 32 parameters were reduced to 10. The 10 parameters were determined analytically from the 9 independent electron-distribution probabilities and 2 macroscopic formal redox potentials. The results showed the presence of a strong positive interaction between a pair of particular hemes. The microscopic formal redox potential changes dramatically with the extent of reduction because of the intramolecular interheme interactions. NMR signals of two hemes were assigned to particular hemes in the crystal structures by nuclear Overhauser effect experiments. The results showed that the hemes with the highest and lowest redox potentials in the one-electron reduction process correspond to hemes I and IV in the crystal structure.

Cytochrome c Group↗
PubMed1990

Redox process of iron-sulfur clusters of the soluble-domain of the membrane-bound hydrogenase from Desulfovibrio vulgaris Miyazaki F studied by resonance Raman spectroscopy.

Resonance Raman spectra of the soluble-domain of a membrane-bound hydrogenase from Desulfovibrio vulgaris Miyazaki F were recorded in different oxidation states. In the oxidized state, the Raman band due to the totally symmetric stretching mode of the iron-sulfur cluster was observed at 341 cm-1, which was attributed to the 3Fe-4S cluster. In the hydrogen-reduced state, only a weak and broad band was observed in its vicinity. During the process of reoxidation, a Raman band assignable to the 4Fe-4S cluster was observed at 333 cm-1 in the first step. Then, the band at 341 cm-1 became stronger and eventually dominated the spectrum. Corresponding changes were observed in the visible absorption spectra of the same sample. It was concluded from these observations that this hydrogenase has both 3Fe-4S and 4Fe-4S clusters and takes on at least three oxidation states, namely, oxidized, intermediate, and hydrogen-reduced ones.

Binding Sites↗
PubMed1986

An epidermal factor which induces thyroid hormone-dependent regression of mesenchymal tissues of the tadpole tail.

Explants of tadpole tail skin secreted a factor which induces the thyroid hormone-dependent regression of the tail mesenchyme. The activity of the factor was not sensitive to digestion with trypsin or pronase. Heating at 120 degrees C but not at 100 degrees C for 20 min destroyed the activity. The factor came out gradually through a dialysis membrane. The factor was retarded on a Sephadex G-10 column and eluted with water after the salts fraction. We suggest that the active principle is a non-proteinaceous substance with a low molecular weight.

Animals↗
PubMed1986

Interrelationship between pituitary and ovarian hormones in normal and neoplastic growth of mammary glands of mice.

While prolactin is a key hormone for normal and neoplastic mammary gland growth, the participation of ovarian estrogen and progesterone is essential for these processes under the normal physiological conditions. Prolactin exerts its influence directly to the glands and indirectly through its luteotropic effects by stimulation of ovarian progesterone secretion. Furthermore, the action of prolactin, whether in promoting normal growth and function or enhancing the progression of neoplastic foci, depends upon the circulating levels of other mammotropic hormones as well as the level of prolactin itself. Presence of estrogen and prolactin is essential for manifestation of progesterone effects on mammary gland growth. Estrogen acts on the mammary glands directly by modulating mammary cell responsiveness to prolactin and indirectly by stimulating pituitary prolactin secretion. While data have been accumulated on the effects of growth hormone on mammary gland growth, the significance of these findings is still unknown. Neoplastic potential of mammary cells is largely dependent upon the susceptibility of the cells to mammotropic hormones.

Animals↗
PubMed1986

Development of pancreatic hyperplasia in female SHN mice receiving ectopic pituitary isografts.

The long-term effects on pancreas of ectopic pituitary grafting at various sites were studied in female SHN mice. Hyperprolactinemia induced by pituitary grafting resulted in an increase in the pancreatic weights, mainly due to hyperplastic proliferation of the pancreatic acinar glands. In addition, islet-cell hyperplasia and adenoma were found in the pituitary-grafted mice. Hyperplastic nodules resembling adenoma of the pancreatic acinar cells were also induced by pituitary grafting. The pancreata of mice with pituitary grafts frequently adhered to the uterus, ovary, and other organs; some of the pancreata further invaded these organs. Control mice bearing no pituitary grafts showed no pancreatic lesions. These results indicate the participation of prolactin in pancreatic tumorigenesis.

Animals↗
PubMed1985

Suppression of normal and preneoplastic mammary growth and uterine adenomyosis with reduced growth hormone level in SHN mice given monosodium glutamate neonatally.

As a step in the evaluation of the role of growth hormone (GH) in mammary tumorigenesis, the effects of neonatal treatment with monosodium glutamate (MSG) on normal and neoplastic mammary growth, plasma levels of GH and prolactin (PRL) and the pattern of estrous cycles were determined in SHN virgin mice. The development of uterine adenomyosis, which is under similar hormonal control, was also examined in these mice. The formation of precancerous mammary hyperplastic alveolar nodules (HAN) was markedly inhibited and the number of 'ghosts', the remnants of regressed HAN, was increased by the single injection of 4 mg MSG on the day of birth, although spontaneous mammary tumorigenesis was not inhibited. The incidence of adenomyosis was suppressed by MSG treatment. Plasma GH level was chronically lower in the MSG-treated mice than in the controls. In contrast, plasma PRL levels and the pattern of estrous cycles were little affected by the treatment. These results indicate an involvement of GH in the development of HAN and uterine adenomyosis in mice.

Animals↗
PubMed1985

Raman scattering from nucleic acids adsorbed at a silver electrode.

Adsorption of nucleic acids at a silver electrode polarized to -0.6 to -0.1 V (vs. Ag/AgCl) was investigated by means of surface enhanced Raman scattering (SERS) spectroscopy. Single-stranded polyriboadenylic acid and thermally denaturated DNA adsorbed at the silver electrode yield two intense bands at 734 and 1335 cm-1 on the SERS spectra. These bands, assigned to the vibrations of adenine residue rings, were much less intense if the SERS spectra were recorded for double-helical complex polyadenylic X polyuridylic acid and native DNA. Moreover, the courses of alkaline denaturation of DNA and its digestion by deoxyribonuclease I were observed by SERS spectroscopy. The results were interpreted as support for the view that intact double-helical segments of nucleic acids are not denatured or destabilized due to their adsorption at the positively charged and roughened surface.

Animals↗
PubMed1985

Interrelationship between prolactin and progesterone in normal mammary gland growth in SHN virgin mice.

In order to clarify the interrelationship between prolactin and progesterone on normal mammary gland growth, SHN strain of virgin mice were given the pituitary grafting under the kidney capsule, the subcutaneous implantation of progesterone pellet or the bilateral ovariectomy singly or in combination at 40 days of age. All mice were killed 60 days after treatments and mammary end-bud formation, mammary DNA content and plasma prolactin level were examined. The single pituitary grafting elevated plasma prolactin levels in both the intact and the ovariectomized animals, however, mammary gland growth was enhanced only in the former. Progesterone pellet implantation also stimulated mammary gland growth in the intact mice, while prolactin changed little. Progesterone effect was nullified by ovariectomy associated with the decline in plasma prolactin level. The simultaneous single pituitary grafting and progesterone pellet implantation in combination or the grafting with three pituitaries restored mammary gland regression by ovariectomy. All findings have demonstrated that the manifestation of progesterone effect on mammary glands is dependent upon prolactin and that the role of prolactin is both direct on the glands and indirect through its luteotropic effect - through its stimulation of ovarian progesterone secretion.

Animals↗
PubMed1985

Temporary increase in the circulating prolactin levels during and after consecutive administration of bromocriptine-mesilate (CB-154) in female mice.

Changes in circulating prolactin (Prl) levels during and after consecutive administration of bromocriptine-mesilate (CB-154; 0.2 mg/day), a potent suppressor of pituitary Prl secretion, were studied in virgin mice of SHN and BALB/c strains. Plasma Prl levels were lower in CB-154-treated SHN mice than in vehicle-treated controls until the first week of the daily treatment. However, the circulating Prl increased in the experimental mice and surpassed the control levels thereafter. The elevated levels of Prl were maintained throughout the treatment, then they decreased to control levels 1 month after the termination of the treatment. In BALB/c mice given CB-154, the pattern of changes of the circulating Prl levels was almost the same seen in SHN mice; a significant suppression of the Prl levels was observed on the 2nd day of the treatment and the levels increased and reached to the control levels thereafter. The results have demonstrated that in mice the inhibition of pituitary Prl secretion by CB-154 did not persist throughout the period of consecutive administration.

Adrenal Glands↗
PubMed1984

Inhibition by hydroxy-N-methyl elliptinium of precancerous mammary hyperplastic alveolar nodule formation in mice.

Daily subcutaneous injections of 5 micrograms hydroxy-N-methyl elliptinium for 4 weeks in a high mammary tumor strain of SHN virgin mice was found to decrease the number of precancerous mammary hyperplastic alveolar nodules (HAN) associated with the increase in the number of ghosts, the remnants of regressed HAN. On the other hand, the treatment had little influence on the normal mammary lobulo-alveolar system, serum prolactin level, estrous cycle and endocrine organ weights. The results have demonstrated that elliptinium can inhibit the formation of HAN and induce their regression with no modulation of endogenous conditions of mammotropic hormones.

Alkaloids↗
PubMed1983

Morphometric synaptology of a whole neuron profile using a semiautomatic interactive computer system.

We propose a new method of dealing with morphometric synaptology that processes all synapses and boutons around the HRP marked neuron on a large composite electron micrograph, rather than a qualitative or a piecemeal quantitative study of a particular synapse and/or bouton that is not positioned on the surface of the neuron. This approach requires the development of both neuroanatomical procedures, by which a specific whole neuronal profile is identified, and valuable specialized tools, which support the collection and analysis of a great volume of morphometric data from composite electron micrographs, in order to reduce the burden of the morphologist. The present report is also concerned with the total and reliable semi-automatic interactive computer system for gathering and analyzing morphometric data that has been under development in our laboratory. A morphologist performs the pattern recognition portion by using a large-sized tablet digitizer and a menu-sheet command, and the system registers the various morphometric values of many different neurons and performs statistical analysis. Some examples of morphometric measurements and analysis show the usefulness and efficiency of the proposed system and method.

Animals↗
PubMed1983

Studies on corticoid action on the toad tadpole tail in vitro.

The effect of adrenal corticoids on the shrinkage of tail segments from Bufo bufo japonicus tadpoles was studied in vitro. Deoxycorticosterone acetate (DCA) was effective in accelerating the shrinkage of tail segments if thyroxine (T4) or triiodothyronine (T3) was present in the medium. The shrinkage caused by DCA was dose dependent. In the absence of thyroid hormone, DCA did not induce tail resorption. Shrinkage of tail segments induced by DCA and T4 was blocked by prolactin. Among the steroid hormones testes in vitro, aldosterone and corticosterone exhibited a potent activity in accelerating shrinkage of tail segments in the presence of T4. The nature of the corticoid action is discussed.

Adrenal Cortex Hormones↗