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Biomedical subjects

T Asada

Publications and source records attributed to T Asada.

At least 163 records · Page 9Linked to original sources
PubMed1986

Analysis of thromboxane B3 converted from eicosapentaenoic acid in human platelet rich plasma by gas chromatography/mass spectrometry.

Gas chromatographic mass spectrometric determination of thromboxane B3 (TXB3) synthesized from platelet is described. Eicosapentaenoic acid (EPA) was added to human platelet rich plasma and after the reaction the exstraction was carried out. Plasma thromboxanes were run through an Amberlite XAD-2 and SEP-PAK silica cartridge, and then chromatographed using silicagel thin layer plate to remove interfering materials, such as 6-keto-prostaglandin F1 alpha. Extracted thromboxanes were converted into the methoxime-dimethylisopropylsilylmethyl ester derivatives and they were measured by gas chromatography/ammonia chemical ionization mass spectrometry. Three peaks were obtained on the gas chromatogram which were presumed to be 3-series metabolite product TXB3 and their related substances. Results indicates the human platelet may easily convert EPA to TXB3 by adding EPA to PRP without adding arachidonic acid.

Ammonia↗
PubMed1980

Calcium regulation in clam foot muscle. Calcium sensitivity of clam foot myosin.

1. The ATPase activity of clam foot myosin alone in the presence of 10 mM MgCl2 was activated approximately ten-fold by 10 muM free calcium ions. The calcium activation was observed in various concentrations of KCl (35-600 mM) and ATO (1 muM-1 mM), and at various pHs (pH 6-9.4). 2. The superprecipitation and ATPase activities of clam foot myosin B were studied by conducting experiments in two different ways. In one of these, the ATP concentration was varied at a fixed concentration of MgCl2, and in the other, the MgCl2 concentration was varied at a fixed concentration of ATP. The following was found: (a) The activities responded in a biphasic manner to change in either the ATP or MgCl2 concentration, giving a peak activity around 10 muM ATP or MgCl2. It is thus suggested that Mg-ATP complex is responsible for both activation and inhibition in the biphasic response. (b) When the ATP or MgCl2 concentration was higher than 100-300 muM, practically no superprecipitation occurred in either the presence or absence of calcium, whereas the ATPase activity was still strongly activated by calcium. 3. Similar results to those described above (a, b) were obtained by using rabbit skeletal actoclam foot myosin in place of clam foot myosin B. Moreover, it was found that as the ATP concentration increased from 1 muM to 1 mM, Mg-ATPase activity of clam foot myosin in the presence of calcium increased in a monophasic manner and that it was as active as actomyosin in the presence of calcium when the ATP concentration was higher than approximately 200 muM. In other words, actin-activation of myosin-ATPase was absent in the ATP concentration where no superprecipitation of actomyosin was observed. 4. Clam foot myosin contained two types of light chain subunits: LCl (17,000 daltons) and LC2 (16,000 daltons). Only LC1 was removed upon washing clam myosin with 10 mM EDTA, and removal of LC1 resulted in loss of the calcium sensitivity of actomyosin-ATPase. 5. In our previous report (J. Biochem. 85, 1543-1546, 1979), it was shown that removal of LC1 from clam foot myosin also resulted in loss of the superprecipitation activity of actomyosin reconstituted from "EDTA-washed" myosin. We now provide further evidence that removal of the regulatory light chain (LC1) results in a reversible uncoupling of ATPase reaction from superprecipitation reaction.

Actomyosin↗