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Biomedical subjects

M Ohe

Publications and source records attributed to M Ohe.

58 records · Page 4Linked to original sources
PubMed1977

Studies on the heterotropic interaction of hemoglobin. I. Mass spectrometric method for determination of the pKa of the beta-146 histidine residue in human hemoglobin.

A mass spectrometric method was developed to determine pH-dependent hydrogen-deuterium exchange at the C-2 position of the imidazole ring of histidine, after converting the amino acid to the methylthiohydantoin derivative. The amount of deuterium exchange in N-acetyl-histidine estimated by the present method was confirmed to be in good agreement with that determined by NMR spectrometry. N-Acetylhistidine was deuterated at various pH's. From the amount of deuterium exchange, a pseudo-first order rate constant (kpsi) was calculated. A pKa value of 7.2 for the amino acid was obtained from the relation between kpsi and pH. This method was applied to estimate the pKa value of beta-146 histidine in human hemoglobin. Human hemoglobin deuterated at various pH's was digested with carboxypeptidase A [EC 3.4.12.2] to release the beta-146 histidine. The amount of deuterium exchange in the isolated histidine was determined to obtain kpsi. From these measurements pKa values of 7.0 for the histidine in oxyhemoglobin and of 8.2 for that in deoxyhemoglobin were found at 36.5 degrees, respectively.

Deuterium↗
PubMed1977

Subunit structure of hemoglobins from erythrocytes of the blood clam, Anadara broughtonii.

Intracellular hemoglobins of the sea blood clam Anadara broughtonii consist of HbI dimer (33%) and HbII tetramer (60%). The molecular weights of globins of HbI and HbII were determined by sodium dodecyl sulfate (SDS)-gel electrophoresis to be 15,500 and 16,500, respectively. The existence of two dissimilar chains, alpha and beta, in globin from HbII tetramer was confirmed electrophoretically and the chains were separated by CM-cellulose chromatography in 8 M urea. In contrast, globin from HbI dimer showed a single band on two types of electrophoresis. The NH2-terminus and the COOH-terminus of HbI were determined to be proline and leucine, respectively. From the results of finger-printing, the alpha and beta chains from HbII were considered to have a rather similar profile, whereas globin from HbI was very different. The results obtained by amino acid analysis of each chain also supported the above findings. It was thus shown that HbII has an alpha2beta2 subunit structure, which is rare among invertebrate hemoglobins. On the other hand, HbI seems to have two identical subunits, designated as "gamma", and to exist as a "gamma2" dimer structure. Both Anadara Hb's appear to have no functional groups relating to the Bohr effect and to be unable to form a binding site for organic phosphates.

Amino Acids↗
PubMedDate not supplied

A technique of scatter-glare correction using a digital filtration.

A scatter-glare correction technique for x-ray images acquired with an antiscatter grid was developed. In the technique, the scatter-glare image was estimated from exposure conditions and subtracted from the acquired image. The basic procedure in the estimation of the scatter-glare image is convolution filtering; however, the novel aspects of the technique are as follows: (1) To estimate the scatter-glare intensity, a formula that does not include the term of object thickness was used. With this formula, the correction can be performed, even for nonuniform phantoms; (2) To estimate the scatter-glare distribution, the experimental scatter-glare point spread function (PSF) was directly used as a convolution kernel. Although the shape of the PSF changed slightly for water thicknesses of 5-25 cm, we applied the PSF measured at a water thickness of 15 cm to the correction experiments. For the stepped water phantom (10-20 cm), scatter-glare estimation produced an average error of 10%, with respect to the lead bar data. Furthermore, the improvement of image quality and quantitative accuracy resulting from the correction was examined.

Biophysical Phenomena↗