Occurrence of thiamin pyrophosphate-dependent 2-oxoglutarate decarboxylase in mitochondria of Euglena gracilis

Abstract2-Oxoglutarate decarboxylase which catalyzes the conversion of 2-oxoglutarate into succinate semialdehyde occurs in mitochondria of Euglena gracilis which lacks a 2-oxoglutarate dehydrogenase complex. The enzyme reaction required thiamin pyrophosphate, MgCl2, 2-mercaptoethanol and NADP+ for the maximum activity, and was not affected by pyruvate and oxalacetate. In the reaction, the enzyme consumed 2-oxoglutarate, evolved CO2 and formed succinate semialdehyde in stoichiometric relationship. The maximum enzyme activity was found at pH 7.0 and 40° C, and Km values for 2-oxoglutarate and thiamin pyrophosphate were 0.33 and 0.056 mM, respectively. These results indicate that the thiamin pyrophosphate-dependent Euglena decarboxylase belongs to a new type of decarboxylase to be designated as 2-oxoglutarate decarboxylase. The probable role of the new decarboxylase in Euglena mitochondria is discussed with regard to the tricarboxylic acid cycle

非回転駆動型の中性子星をもつ超新星残骸の「すざく」による研究

学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 梶田 隆章, 東京大学教授 半場 藤弘, 東京大学准教授 茂山 俊和, 東京大学教授 中畑 雅行, 東京大学教授 山本 智University of Tokyo(東京大学

A lattice attenuation in Cds measured by the ultrasonic injection method

This paper concerns the use of Brillouin scattering measurements to study lattice attenuation in semiconducting CdS crystals. Measured acoustic fluxes are produced by the acoustoelectric domains. In order to measure the attenuation constant, an ultrasonic injection method is applied. A sample is divided into two parts; one part is used as a generation region of the acoustic flux [region (1)] and the other part is used as a propagation region of the injected flux [region (2)]. The acoustic attenuations of various frequencies are measured at region (2). The lattice attenuation is greatly affected by the rise time of an applied pulse in region (1). It is clear that acoustic flux in the acoustic domain which originates from the amplification of the pure thermally excited acoustic flux attenuates as f2 and is in accordance with the Akhieser loss. On the other hand, a shock-excited acoustic flux attenuates as f ∼1.5

Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission

Supernova remnants (SNRs) retain crucial information about both their parent explosion and circumstellar material left behind by their progenitor. However, the complexity of the interaction between supernova ejecta and ambient medium often blurs this information, and it is not uncommon for the basic progenitor type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here we present a powerful new observational diagnostic to discriminate between progenitor types and constrain the ambient medium density of SNRs solely using Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs and detect Fe K alpha emission from 23 young or middle-aged remnants, including five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in Type Ia remnants being significantly less ionized than in core-collapse SNRs. Within each progenitor group, the Fe K alpha luminosity and centroid are well correlated, with more luminous objects having more highly ionized Fe. Our results indicate that there is a strong connection between explosion type and ambient medium density, and suggest that Type Ia supernova progenitors do not substantially modify their surroundings at radii of up to several parsecs. We also detect a K-shell radiative recombination continuum of Fe in W49B and IC 443, implying a strong circumstellar interaction in the early evolutionary phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur