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Biomedical subjects

T Iwasa

Publications and source records attributed to T Iwasa.

At least 73 records · Page 4Linked to original sources
PubMed1985

Dephosphorylation of microtubule-associated protein 2, tau factor, and tubulin by calcineurin.

Calcineurin dephosphorylated microtubule-associated protein 2 (MAP2) and tau factor phosphorylated by cyclic AMP-dependent and Ca2+, calmodulin-dependent protein kinases from the brain. Tubulin, only phosphorylated by the Ca2+, calmodulin-dependent protein kinase, served as substrate for calcineurin. The concentrations of calmodulin required to give half-maximal activation of calcineurin were 21 and 16 nM with MAP2 and tau factor as substrates, respectively. The Km and Vmax values were in ranges of 1-3 microM and 0.4-1.7 mumol/mg/min, respectively, for MAP2 and tau factor. The Km value for tubulin was in a similar range, but the Vmax value was lower. The peptide map analysis revealed that calcineurin dephosphorylated MAP2 and tau factor universally, but not in a site-specific manner. The autophosphorylated Ca2+, calmodulin-dependent protein kinase was not dephosphorylated by calcineurin. These results suggest that calcineurin plays an important role in the functions of microtubules via dephosphorylation.

Animals↗
PubMed1984

Ca2+, calmodulin-dependent phosphorylation, and inactivation of glycogen synthase by a brain protein kinase.

Glycogen synthase from skeletal muscle was phosphorylated by a Ca2+, calmodulin-dependent protein kinase from brain, with concomitant inactivation. About 0.7 mol phosphate/mol subunit was sufficient for a maximal inactivation of glycogen synthase. Further phosphorylation of the enzyme had no effect on the activity. The concentrations required to give half-maximal phosphorylation and inactivation of glycogen synthase were 1.1 and 0.5 microM for Ca2+, and 22 and 11 nM for calmodulin, respectively. The molar ratio of the subunit of the protein kinase to calmodulin was 2-3:1 for half-maximal phosphorylation and inactivation of glycogen synthase. The Km values for glycogen synthase and ATP were 3.6 and 114 microM, respectively, for phosphorylation. Phosphate was incorporated into sites Ia, Ib, and 2 on glycogen synthase, and site 2 was the most rapidly phosphorylated. These results indicate that the brain Ca2+, calmodulin-dependent protein kinase is probably involved in glycogen metabolism in the brain as a glycogen synthase kinase.

Adenosine Triphosphate↗
PubMed1984

Phosphorylation and activation of calmodulin-sensitive cyclic nucleotide phosphodiesterase by a brain Ca2+, calmodulin-dependent protein kinase.

A Ca2+, calmodulin-dependent protein kinase from rat brain with a MW of 640,000 phosphorylated calmodulin-sensitive phosphodiesterase from the brain cytosol. The Km of the enzyme for the phosphodiesterase was 5.0 microM and the Vmax was 212 nmol/mg/min. The amount of phosphate incorporated into the phosphodiesterase was 0.7 mol/mol subunit. Phosphorylation of the phosphodiesterase enhanced the enzyme activity by about 20% for hydrolysis of a higher concentration of cyclic AMP.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Ca2+, calmodulin-dependent phosphorylation of glycogen synthase by a brain protein kinase.

A Ca2+, calmodulin-dependent protein kinase from brain with a Mr of 640 000 is capable of phosphorylating glycogen synthase from skeletal muscle. The reaction was inhibited by the addition of 1 mM EGTA and 50 microM trifluoperazine, but not by protein kinase inhibitor and heparin. The amount of phosphate incorporated into glycogen synthase was 1.4 mol/mol subunit. The phosphorylation sites of glycogen synthase were cyanogen bromide-treated peptides CB-1 and CB-2 and only the seryl residue was phosphorylated.

Animals↗
PubMed1983

A high-affinity (Ca2+ + Mg2+)-ATPase in plasma membranes of rat ascites hepatoma AH109A cells.

The activity of calcium-stimulated and magnesium-dependent adenosinetriphosphatase which possesses a high affinity for free calcium (high-affinity (Ca2+ + Mg2+)-ATPase, EC 3.6.1.3) has been detected in rat ascites hepatoma AH109A cell plasma membranes. The high-affinity (Ca2+ + Mg2+)-ATPase had an apparent half saturation constant of 77 +/- 31 nM for free calcium, a maximum reaction velocity of 9.9 +/- 3.5 nmol ATP hydrolyzed/mg protein per min, and a Hill number of 0.8. Maximum activity was obtained at 0.2 microM free calcium. The high-affinity (Ca2+ + Mg2+)-ATPase was absolutely dependent on 3-10 mM magnesium and the pH optimum was within physiological range (pH 7.2-7.5). Among the nucleoside trisphosphates tested, ATP was the best substrate, with an apparent Km of 30 microM. The distribution pattern of this enzyme in the subcellular fractions of the ascites hepatoma cell homogenate (as shown by the linear sucrose density gradient ultracentrifugation method) was similar to that of the known plasma membrane marker enzyme alkaline phosphatase (EC 3.1.3.1), indicating that the ATPase was located in the plasma membrane. Various agents, such as K+, Na+, ouabain, KCN, dicyclohexylcarbodiimide and NaN3, had no significant effect on the activity of high-affinity (Ca2+ + Mg2+)-ATPase. Orthovanadate inhibited this enzyme activity with an apparent half-maximal inhibition constant of 40 microM. The high-affinity (Ca2+ + Mg2+)-ATPase was neither inhibited by trifluoperazine, a calmodulin-antagonist, nor stimulated by bovine brain calmodulin, whether the plasma membranes were prepared with or without ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid. Since the kinetic properties of the high-affinity (Ca2+ + Mg2+)-ATPase showed a close resemblance to those of erythrocyte plasma membrane (Ca2+ + Mg2+)-ATPase, the high-affinity (Ca2+ + Mg2+)-ATPase of rat ascites hepatoma cell plasma membrane is proposed to be a calcium-pumping ATPase of these cells.

Animals↗
PubMed1983

Comparison of high affinity Ca2+-ATPase and low affinity Ca2+-ATPase in rat liver plasma membranes.

Rat liver plasma membranes contained two types of calcium-dependent adenosine triphosphatase (Ca2+-ATPase, EC 3.6.1.3) activities. One of them had a high affinity for free calcium (Ca2+) with an apparent half maximal saturation constant (K0.5) of 0.2 microM (high affinity Ca2+-ATPase), and the other exhibited a low affinity with a K0.5 of 50 microM for Ca2+ (low affinity Ca2+-ATPase). The high affinity Ca2+-ATPase showed: independence from free magnesium (Mg2+), a wide range of optimum pH (7.2-7.5), inhibition by a large amount of calmodulin, and substrate preference for ATP, GTP and ITP. On the other hand, the low affinity Ca2+-ATPase showed: stimulation by Mg2+ as well as Ca2+, an optimum pH of 8, mild stimulation by calmodulin, reversible inhibition by calmodulin-antagonists, inhibition by dicyclohexylcarbodiimide, and substrate preference for UTP and GTP. Both Ca2+-ATPases were insensitive to Na+, K+, ouabain, NaN3 and KCN. Orthovanadate, a potent inhibitor for many ATPases, had no effect on both ATPases over a wide range of concentrations (7 nM-1.7 mM). The Ca2+-ATPases could be separated by gel filtration on a Sepharose 4B column after solubilization with Triton X-100. The high affinity Ca2+-ATPase showed a Stokes radius of about 49 A and a sedimentation coefficient of about 7.0 S with a molecular weight of 1.4 X 10(5). The frictional ratio was 1.4. The results suggest that the high affinity Ca2+-ATPase may be a possible candidate for an ATPase with Ca2+ pumping activity, and that the high affinity enzyme is distinct from the low affinity Ca2+-ATPase in the rat liver plasma membranes.

Animals↗
PubMed1982

Photoreaction of tyrosine-iodinated bacteriorhodopsin at low temperature.

To elucidate the role of tyrosine residues in the shift of lambda max and the light-driven proton pump of bacteriorhodopsin, the photochemical reaction of tyrosine-iodinated bacteriorhodopsin (tyr-mod-bR) was investigated by low-temperature spectrophotometry. After 4-5 of 11 tyrosine residues of bacteriorhodopsin were iodinated, the meta-intermediate of tyr-mod-bR in 75% glycerol solution became so stable that its decay could be observed even at room temperature and it was stable in the dark for several hours at -65 degrees C. Four batho-intermediates were formed by irradiation with green light (500 nm) at -170 degrees C. Like native bacteriorhodopsin, these batho-intermediates were photoreversible at -170 degrees C. Four corresponding meta-intermediates were also formed by irradiation at -60 degrees C. Using the difference spectra between meta-intermediates and tyr-mod-bR, the absorption spectra of four kinds of tyr-mod-bRs, batho-intermediates, and meta-intermediates were estimated. Each was at shorter wavelengths than that of its corresponding type in native bacteriorhodopsin. The results indicate that two or more tyrosine residues have some role in determining color in native bacteriorhodopsin.

Bacteriorhodopsins↗
PubMed1982

[Comparison of 201T1-chloride and 67Ga-citrate in thyroid tumor scintigraphy].

Twenty-five patients with thyroid tumors were examined by 201T1-chloride and 67Ga-citrate scintigraphy heterochronously in our department. All cases showed the cold nodule with 131I or 99mTc-pertechnetate thyroid scintigraphy and each one was given a histological diagnosis after surgery or excisional biopsy. In 15 cases of thyroid carcinoma, 12 (80%) were positive by 201T1-chloride; 4 (26.7%) were positive by 67Ga-citrate. In examining each histological type, 8 of 9 cases of papillary carcinoma (88.9%) were positive by 201T1-chloride. In 1 negative case the tumor was almost completely encysted; however, they were all negative by 67Ga-citrate. In 2 patients with follicular carcinoma, both of them revealed a positive figure by 201T1-chloride, and one of these with oxyphilic cell carcinoma showed a positive figure by 67Ga-citrate. In 1 case of medullary carcinoma there was slight accumulation with 201T1-chloride, but there was no accumulation with 67Ga-citrate. In 3 cases of undifferentiated carcinoma, 2 patients with small carcinoma showed a negative figure by 201T1-chloride. However, they all showed a positive figure using 67Ga-citrate and this medium also disclosed distant metastases of undifferentiated carcinoma. In 10 patients with thyroid adenoma, 3 (30%) showed a positive figure by 201T1-chloride. Histologically, these were all tubular adenoma, but in all cases of thyroid adenoma 67Ga-citrate revealed a negative figure. From the above mentioned results, the following conclusion were reached. Tumors showing a positive figure by 201T1-chloride that elicited negative results using 67Ga-citrate proved to be differentiated carcinoma or low differentiated types of adenoma. Surgery is indicated in these cases. All of the tumors revealing a positive figure by 67Ga-citrate were highly malignant types. If these tumors showed a negative figure when 201T1-chloride was used, undifferentiated carcinoma was suggested. In undifferentiated carcinoma, 67Ga-citrate scintigraphy is a useful procedure in locating distant metastases, in determining the area to be irradiated, and in judging the effect of therapy.

Adenocarcinoma↗
PubMed1981

[Biological activity of prostaglandin E1 derivative, ONO-802 on smooth muscle (author's transl)].

The effects of prostaglandin (PG) E1 derivative, 16,16-dimethyl-trans-delta-2PGE1 methyl ester (ONO-802) on the rat stomach fundal strip, uterus and ileum were studied. Its substrate specificity for 15-hydroxy prostaglandin dehydrogenase (PGDH) was also examined. Contractions were recorded isometrically by superfusion method. PGE1, E2, and F2 alpha caused maximal contraction of the fundal strip immediately after application and relaxation to the original state within 10 min. Contractile pattern of the fundal strip produced by ONO-802 was quite specific and different from those by classic PGs. Contraction was increased slowly to its maximum in 10 to 20 min after application of ONO-802 and thereafter returned to the original state in 20 to 40 min. Contractive response of the rat ileum to ONO-802 was a gradual increase of the tonus and restoration in more than 120 min after reaching its maximal tonus. The rat uterus responded to 1 microgram of ONO-802 with double maximal contraction amplitude of spontaneous activity, with increased contraction amplitude restored in 90 min. In a combination of ONO-802 with PGE1, E2 and F2 alpha, the contractile response of the fundal strip to ONO-802 was masked by the actions of classic PGs and additional potentiation was not observed. Contractive activity of ONO-802 was not reduced by placental PGDH.

Alprostadil↗
PubMed1981

[Effectiveness of acetylspiramycin for Mycoplasma pneumonia in children (author's transl)].

The clinical efficacy and safety of acetylspiramycin for Mycoplasma pneumonia in children were studied at a dose level of 50 mg/kg/day q.i.d. and the following results were obtained. Acetylspiramycin showed effect in 24 patients out of 25 (96.0%). The level of transminase was increased in 3 cases on admission. One of them was an uneffective case, and eruption was seen after administrating the drug. Diarrhea and poor appetite were observed in one case as side effects, and they were controlled easily. It may be concluded from these results acetylspiramycin was relatively free from side effects and considered to be useful for Mycoplasma pneumonia.

Age Factors↗
PubMed1981

Application of live attenuated measles and mumps vaccines in children with acute leukemia.

Eight children with acute leukemia in remission were immunized with live attenuated measles vaccine and 4 with mumps vaccine. Immunological examinations before vaccination showed that the numbers of white blood cells, percentages of lymphocytes, levels of immunoglobulins and responses to skin tests with DNCB, PPD, PHA and varicella antigen were within normal ranges in most of these children. Chemotherapy against leukemia was stopped for 2 weeks, from one week before to one week after vaccination. One child had a transient fever 10 days after measles vaccination, but no side reactions were observed in the others. Seroconversion was observed in all but one child who received measles vaccine, and neutralizing antibodies have persisted for at least 4 weeks and at most 3 years, when this study was terminated.

Acute Disease↗
PubMed1980

Formation of 9-cis- and 11-cis-retinal pigments from bacteriorhodopsin by irradiating purple membrane in acid.

Both light-adapted and dark-adapted forms of bacteriorhodopsin in purple membrane in 67% glycerol solution were allowed to stand in acidic conditions by the addition of HCl to final concentrations from 4 X 10(-4) to 2 X 10(-2) M for 24 h at 3 degrees C. Over this concentration range, the acid-induced products from both species showed a maximum absorbance around 600 nm and high-performance liquid chromatography of extracted retinal isomers revealed that the acid-induced form of bacteriorhodopsin has 13-cis- and all-trans-retinals in a molar ratio of 4:6, which is intermediate between those of the dark-adapted and the light-adapted forms at neutral pH values. Exposure of the acid-induced form of bacteriorhodopsin to light at wavelengths longer than 670 nm at 3 degrees C caused a decrease of the absorbance around 600 nm with a concomitant rise of the absorbance around 500 nm. The extract from the irradiated products of bacteriorhodopsin in acid contained 9-cis- and 11-cis-retinals in addition to 13-cis- and all-trans-retinals. The absorbance maximum estimated from the analysis of the absorption spectra and the composition of the isomers was found at 495 nm for the 9-cis-retinal pigment and around 560 nm for the 11-cis-retinal pigment. On irradiation with 438-nm light, the 9-cis-retinal pigment disappeared with a concomitant increase of both the 13-cis- and all-trans-retinal pigments as judged by chromophore analysis and the absorption spectrum. The 9-cis-retinal pigment brought to pH 9 exhibited a maximum absorbance at 450 nm; this could be decomposed by the action of hydroxylamine or converted to a form resembling normal bacteriorhidopsin by 438-nm irradiation.

Bacteriorhodopsins↗