Biomedical subjects

Masaki Mishima

Publications and source records attributed to Masaki Mishima.

21 records · Page 2Linked to original sources

PubMed2003

[Usefulness of rapid quantitative cardiac troponin T and myoglobin assays for the diagnosis of acute myocardial infarction].

BACKGROUND AND OBJECTIVES: The rapid cardiac troponin T (cTnT) test is widely used to detect myocardial necrosis in the emergency setting. This assay system is rapid and myocardial-specific, but the plasma cTnT concentration is difficult to determine quantitatively. A recently developed bedside cTnT and myoglobin (Mb) analyzer (CARDIAC system) was evaluated. METHODS: The new CARDIAC system was used to measure plasma cTnT and Mb levels, and serum levels of creatine kinase MB isoenzyme (CK-MB), cTnT and Mb were measured by conventional assays in 160 consecutive emergency patients with suspected acute myocardial infarction. RESULTS: The sensitivity of cTnT for identifying acute myocardial infarction was 76%, significantly higher than that of Mb (67%, p < 0.01) and CK-MB (54%, p < 0.05). The diagnostic sensitivities in patients admitted < or = 3 hr and 3-6 hr after onset were 52% and 65% for cTnT, 60% and 90% for Mb, and 36% and 50% for CK-MB, respectively. These sensitivities of Mb were significantly higher than those of CK-MB but not cTnT. However, the sensitivity of cTnT (100%) was significantly higher than that of Mb (58%, p < 0.01) and CK-MB (70%, p < 0.001) in patients admitted > 6 hr after onset. The specificities of cTnT, Mb and CK-MB were 96%, 76% (p < 0.001 vs cTnT and CK-MB) and 95%, respectively. Therefore, cTnT (86%) had significantly (p < 0.001) higher diagnostic accuracy compared with Mb (71%) and CK-MB (75%). Combination diagnosis using cTnT and Mb showed the highest sensitivity (86%) compared with cTnT (p < 0.05) and Mb (p < 0.001). The correlation coefficients between the levels measured by CARDIAC system and those by ordinary assays were 0.98 in cTnT and 0.97 in Mb. CONCLUSIONS: Bedside rapid quantitative assays of cTnT and Mb are useful as a point of care test for the diagnosis of acute myocardial infarction.

Aged↗

PubMed2002

Role of tryptophan residues in the recognition of mutagenic oxidized nucleotides by human antimutator MTH1 protein.

The human MTH1 antimutator protein hydrolyzes mutagenic oxidized nucleotides, and thus prevents their incorporation into DNA and any subsequent mutation. We have examined its great selectivity for oxidized nucleotides by analyzing the structure of the protein and its interaction with nucleotides, as reflected in the fluorescence of its tryptophan residues. The binding of nucleotides decreased the intensity of MTH1 protein fluorescence and red-shifted the emission peak, indicating that at least one tryptophan residue is close to the binding site. Oxidized nucleotides (2-OH-dATP and 8-oxo-dGTP) produced a larger decrease in fluorescence intensity than did unoxidized nucleotides, and MTH1 protein had a much higher binding affinity for oxidized nucleotides. Deconvolution of protein fluorescence by comparison of its quenching by positively (Cs(+)) and negatively (I(-)) charged ions indicated that the MTH1 tryptophan residues are in two different environments. One class of tryptophan residues is exposed to solvent but in a negatively charged environment; the other class is partially buried. While the binding of unoxidized nucleotides quenches the fluorescence of only class 1 tryptophan residue(s), the binding of oxidized nucleotides quenched that of class 2 tryptophan residue(s) as well. This suggests that selectivity is due to additional contact between the protein and the oxidized nucleotide. Mutation analysis indicated that the tryptophan residue at position 117, which is in a negative environment, is in contact with nucleotides. The negatively charged residues in the binding site probably correlate with the finding that nucleotide binding requires metal ions and depends upon their nature. Positively charged metal ions probably act by neutralizing the negatively charged nucleotide phosphate groups. (c) 2002 Elsevier Science Ltd.

Adaptor Proteins, Signal Transducing↗

PubMed2001

A molecular basis for the selective recognition of 2-hydroxy-dATP and 8-oxo-dGTP by human MTH1.

MTH1 hydrolyzes oxidized purine nucleoside triphosphates such as 8-oxo-dGTP, 8-oxo-dATP, 2-hydroxy-dATP, and 2-hydroxy rATP to monophosphates, and thus avoids errors caused by their misincorporation during DNA replication or transcription, which may result in carcinogenesis or neurodegeneration. This substrate specificity for oxidized purine nucleoside triphosphates was investigated by mutation analyses based on the sequence comparison with the Escherichia coli homolog, MutT, which hydrolyzes only 8-oxo-dGTP and 8-oxo-rGTP but not oxidized forms of dATP or ATP. Neither a replacement of the phosphohydrolase module of MTH1 with that of MutT nor deletions of the C-terminal region of MTH1, which is unique for MTH1, altered the substrate specificity of MTH1. In contrast, the substitution of residues at position Trp-117 and Asp-119 of MTH1, which showed apparent chemical shift perturbations with 8-oxo-dGDP in NMR analyses but are not conserved in MutT, affected the substrate specificity. Trp-117 is essential for MTH1 to recognize both 8-oxo-dGTP and 2-hydroxy-dATP, whereas Asp-119 is only essential for recognizing 2-hydroxy-dATP, thus suggesting that origins of the substrate-binding pockets for MTH1 and MutT are different.

Adaptor Proteins, Signal Transducing↗