Studies on the subsite structure of amylases. III. Inhibition by gluconolactone of the hydrolysis of maltodextrin catalyzed by glucoamylase from Rhizopus niveus

Inhibition by gluconic acid-1 : 5-lactone (gluconolactone) and phenyl alpha-glucoside of the hydrolysis of maltodextrin catalyzed by glucoamylase [EC 3.2.1.3] from Rhizopus niveus was investigated in relation to the subsite structure of the enzyme. Inhibition by gluconolactone was of the mixed type, whereas that by phenyl alpha-glucoside was purely competitive. These inhibition types were consistent with a theoretical prediction based on the assumption that gluconolactone and phenyl alpha-glucoside bind mainly to Subsites 1 and 2, respectively. The inhibitor constant of gluconolatone was determined to be 1.5 mM, which is in good agreement with the dissociation constant estimated by difference spectrophotometry (1.5 mM) (Ohnishi, M, et al. (1975) J. Biochem, 77, 695-703).     

Production of vitamin B12 in genetically engineered Propionibacterium freudenreichii

Since the chemical synthesis of vitamin B12 requires more than 70 steps, the production of vitamin B12 has been achieved by microorganism fermentation with additional brief chemical modifications. In an effort to increase the productivity of vitamin B12, we tried to express 10 genes belonging to the hem, cob and cbi gene families involved in the synthesis of vitamin B12 in Propionibacterium freudenreichii, which is a known producer of vitamin B12. In a recombinant P. freudenreichii clone that harbored the expression vector containing a cobA, cbiLF, or cbiEGH, we obtained an increase in vitamin B12 production of 1.7-, 1.9-, and 1.5-fold higher, respectively, than that in the microorganism without any cloned genes in the expression vector pPK705. The cobU and cobS genes caused a slight increase in the production of vitamin B12. Furthermore, we achieved multigene expression in P. freudenreichii. In a recombinant P. freudenreichii clone that harbored an exogenous gene, hemA, from Rhodobacter sphaeroides and endogenous hemB and cobA genes, we successfully achieved the production of about 1.7 mg/l vitamin B12, 2.2-fold higher than that produced by P. freudenreichii harboring pPK705.     

Self-assembly of a silica-surfactant nanocomposite in a porous alumina membrane

A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies.     

Analysis of fumonisin B1 and B2 in beer and raw materials of beer by liquid chromatography/tandem mass spectrometry

A simple method for analysis of fumonisin B1 (FB1) and fumonisin B2 (FB2) in beer and raw materials of beer using liquid chromatography-electrospray ionization tandem mass spectrometry (LC/MS/MS) was developed. Samples were prepared and purified by using solid-phase extraction columns (SAX). The LC separation was performed with an octadecylated silica column at a flow-rate of 0.2 mL/min, using a mobile phase consisting of water and acetonitrile. MS/MS was used in multiple reaction monitoring, employing electrospray ionization (ESI-MRM). Recoveries of spiked FB1 and FB2 from beer were 64% and 52%, respectively, at the level of 5 microg/kg. Recoveries of spiked FB1 and FB2 from malt, cornstarch, and corn grit, at the level of 50 microg/kg, were 87.9% and 86.4%, 89.5% and 87.9%, 86.6% and 81.1%, respectively. This method may have applications in quality assurance.     

Analysis of trichothecenes in barley tea and beer by liquid chromatography/tandem mass spectrometry

A simple method for analysis of trichothecenes [Type A: diacetoxyscirpenol, neosolaniol, HT-2 toxin, and T-2 toxin, Type B: deoxynivalenol, nivalenol, fusarenon-X, 3-acetyldeoxynivalenol, 15-acetyldeoxynivarenol] in barley tea and beer using liquid chromatography tandem mass spectrometry (LC/MS/MS) was developed. Trichothecenes were extracted with ethyl acetate-methanol (19:1). The solvent was evaporated to dryness and the residue was dissolved in water-methanol (3:1) for injection into the LC/MS/MS. The LC separation was performed with an octadecylated silica column at a flow-rate of 0.2 mL/min, using a mobile phase consisting of water, methanol and acetonitrile. MS/MS was used in multiple reaction monitoring, employing electrospray ionization (ESI-MRM). The recoveries of trichothecenes from drinks at 1 microg/L (Type A) and 10 microg/L (Type B) were 52.5-115.2% (barley tea) and 68.1-127.5% (beer). Five barley tea and ten beer samples were analyzed by this method. Trichothecenes were not detected in them. This method may have applications in quality assurance.     

Thermoelectric properties of p- and n-type FeSi2 prepared by spray drying, compaction and sintering technique

FeSi₂ alloys doped with Mn and Co (p-type Fe_0.926Mn_0.074Si₂, n-type Fe_0.980Co_0.020Si₂) were prepared by vacuum induction melting. The ingots were pulverized in a jet-mill, and the powders were granulated by spray drying method using aqueous polyvinyl alcohol (PVA) binder in order to investigate the possibility of production on a large scale. The powders granulated exhibited excellent characteristics of flowability, leading to the smooth feeding into a die cavity in compacting. The powders obtained were compacted at a pressure of 98 MPa. It was debindered at 723 K for 1 h and sintered at 1423 K for 5 h in a hydrogen atmosphere, so that the residual carbon and oxygen contents in a sintered body approached to those in the starting powder. Subsequently it was annealed at 1113 K for 100 h in an argon atmosphere, to produce the semiconducting -FeSi₂ phase. The thermoelectric figures of merit (Z) for optimum p- and n-type FeSi₂ are 1.75 × 10^–4 (K^–1) and 2.0 × 10^–4 (K^–1) at about 900 K, respectively, which agree roughly with those obtained by Tani and Kido for FeSi₂ materials prepared by the spark plasma sintering method. It indicates that the spray drying method leading to the production on a large scale is available for the fabrication of the thermoelectric FeSi₂ materials.     

Optical topography: practical problems and new applications

We will briefly review the present status of optical topography and then discuss the method of improving practicality, i.e., the signal-to-noise (S/N) ratio and the spatial resolution in observations of higher-order brain functions. The optimum wavelength pair improved the S/N ratio sixfold for deoxyhemoglobin, and new configurations of light irradiation and detection positions doubled the spatial resolution. We also report on developing application fields of optical topography. This modality will bridge the gap between natural sciences, neuroscience, and pedagogy, and show actual real-time brain activity.     

Production and performance of the inFOCmicroS 20-40-keV graded multilayer mirror

The International Focusing Optics Collaboration for microCrab Sensitivity (InFOCmicroS) balloonborne hard x-ray telescope incorporates graded Pt/C multilayers replicated onto segmented Al foils to obtain the significant effective area at energies previously inaccessible to x-ray optics. Reflectivity measurements of individual foils demonstrate our capability to produce a mass quantity of multilayered foils with a rms roughness of 0.5 nm. The effective area of the completed mirror is 78 and 22 cm2 at 20 and 40 keV, respectively. The measured half-power diameter is 2.0 +/- 0.6 are min (90% confidence). The successful completion of this mirror demonstrates its applicability to future x-ray telescopes such as Constellation-X.