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Articles by M Ohta
Total Records ( 3 ) for M Ohta
  R Akagi , Y Takai , M Ohta , H Kanehisa , Y Kawakami and T. Fukunaga

Objective: the present study examined which of muscle volume (MV) and cross-sectional area (CSA) is appropriate for evaluating the relation with elbow flexor muscle strength in young and elderly individuals.

Methods: the subjects were 52 young (20–34 year; 30 men and 22 women) and 51 elderly individuals (60–77 year, 19 men and 32 women). The MV and maximal anatomical CSA (ACSA) of elbow flexors were determined by magnetic resonance imaging. The torque developed during maximal voluntary contraction of isometric elbow joint flexion was converted to force by dividing it by the forearm length of each subject.

Results: torque was significantly correlated with MV in young and elderly individuals (r = 0.564–0.926). Similarly, force was also significantly correlated with ACSA in each of them (r = 0.637–0.906). However, the y-intercepts of the regression lines for the ACSA-force relationship in young men and women were significantly higher than zero. There was no age effect on torque per MV, whereas force per ACSA was significantly higher in young adults than in elderly individuals.

Conclusion: for elbow flexors, MV compared to ACSA is appropriate for evaluating the size–strength relationship and the existence of age-related difference in muscle strength per size.

  N Kasai , S Ikushiro , S Hirosue , A Arisawa , H Ichinose , Y Uchida , H Wariishi , M Ohta and T. Sakaki

We cloned full-length cDNAs of 130 cytochrome P450s (P450s) derived from Phanerochaete chrysosporium and successfully expressed 70 isoforms in Saccharomyces cerevisiae. To elucidate substrate specificity of P. chrysosporium P450s, we examined various substrates including steroid hormones, several drugs, flavonoids and polycyclic aromatic hydrocarbons using the recombinant S. cerevisiae cells. Of these P450s, two CYPs designated as PcCYP50c and PcCYP142c with 14% identity in their amino acid sequences catalyse 3'-hydroxylation of flavone and O-deethylation of 7-ethoxycoumarin. Kinetic data of both enzymes on both reactions fitted not to the Michaelis–Menten equation but to Hill’s equation with a coefficient of 2, suggesting that two substrates bind to the active site. Molecular modelling of PcCYP50c and a docking study of flavone to its active site supported this hypothesis. The enzymatic properties of PcCYP50c and PcCYP142c resemble mammalian drug-metabolizing P450s, suggesting that their physiological roles are metabolism of xenobiotics. It is noted that these unique P. chrysosporium P450s have a potential for the production of useful flavonoids.

  Y Takaoka , M Ohta , A Takeuchi , K Miura , M Matsuo , T Sakaeda , A Sugano and H. Nishio

UDP-glucuronosyltransferase 1A1 (UGT1A1) is an endoplasmic reticulum membrane protein that catalyses glucuronidation. Mutant UGT1A1 possesses a different conjugation capacity, and the molecular mechanisms regulating these conjugation reactions are as yet unclear. To elucidate these molecular mechanisms, we simulated and analysed the glucuronidation of wild-type UGT1A1 and six UGT1A1 mutants, with bilirubin as the substrate. We found that only the orientation of the substrates correlated with the conjugation capacity in in vitro experiments. Inasmuch as glucuronidation is an intermolecular rearrangement reaction, we find that the conjugation reaction proceeds only when the hydroxyl group of the substrate is oriented towards the coenzyme, which allows the proton transfer to occur.

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