The Emi2 Protein of Saccharomyces cerevisiae is a Hexokinase Expressed under Glucose Limitation

Hexokinases catalyze glucose phosphorylation at the first step in glycolysis in eukaryotes. In the budding yeast Saccharomyces cerevisiae , three enzymes for glucose phosphorylation have long been known: Hxk1, Hxk2, and Glk1. In this study, we focus on Emi2, a previously uncharacterized hexokinase-like protein of S. cerevisiae . Our data show that the recombinant Emi2 protein (rEmi2), expressed in Escherichia coli , possesses glucose-phosphorylating activity in the presence of ATP and Mg ²⁺ . It was also found that rEmi2 phosphorylates not only glucose but also fructose, mannose and glucosamine in vitro . In addition, we examined changes in the level of endogenous Emi2 protein in S. cerevisiae in the presence or absence of glucose and a non-fermentable carbon source. We found that the expression of Emi2 protein is tightly suppressed during proliferation in high glucose, while it is strongly upregulated in response to glucose limitation and the presence of a non-fermentable carbon source. Our data suggest that the expression of the endogenous Emi2 protein in S. cerevisiae is regulated under the control of Hxk2 in response to glucose availability in the environment.     

Proposal for st-Routing Protocol

A routing protocol chooses one of the several paths (routes) from a source node to a destination node in the computer network, to send a packet of information. In this paper, we propose a new routing protocol, which we call st-routing protocol, based on st-numbering of a graph. The protocol fits well in noisy environments where robustness of routing using alternative paths is a major issue. The proposed routing protocol provides a systematic way to retry alternative paths without generating any duplicate packets. The protocol works for only those networks that can be represented by biconnected graphs.     

Trace elements in human transitory milk. Variation caused by biological attributes of mother and infant

Multielement analysis was performed on human milk collected on 5-9-d postpartum from 51 Japanese females using inductively coupled plasma (ICP) mass spectrometry (MS), ICP atomic emission spectrometry (ICP-AES) and fluorometry. Thirty-one elements were detected by these analytical methods in milk. Twelve elements (Na, Mg, P, S, K, Ca, Cu, Zn, Se, Sr, Rb, and Mo) were detected in all of the samples. Al, Cs, and Ba were the elements detected by ICP-MS in more than half of the samples. Multiple regression analysis extracted biological attributes of mother and infant, such as maternal stature, maternal wt, or infant's birth wt, as statistically significant factors contributing to the variation in elemental concentration in milk. However, the rates of contribution were small in all cases. It was concluded that the biological attributes of mother and infant examined in this study were not the major factors that contribute to elemental variation in human milk.     

In situ TEM study on changes in structure and electrical conductance of carbon nanotube-gold contact induced by local joule heating

Electrical conductance of multi-walled carbon nanotubes (MWCNTs) with closed and open tips contacting with a gold (Au) electrode was studied by in situ transmission electron microscopy. When a current density through the contact region reached a threshold value of 2.6 × 10⁸ A/cm², the MWCNT tip was embedded into the Au surface by local melting of Au, and the total resistance was reduced with the increase of the contact area. Conductance per unit area at the contact between the MWCNT and Au electrode for the open-ended MWCNT is four times larger than that for the close-ended one, which is due to the direct connection of inner walls of the open-ended MWCNT with the Au surface.     

Molecular breeding of cellulolytic microbes, plants, and animals for biomass utilization

Cellulosic materials are the major components of fibrous biomass produced as a result of photosynthesis and are considered as a reservoir of solar energy and organic materials. In order to cope with the problems of food and energy shortages expected in the near future, biotechnologists are encouraged to develop new technologies for the more effective utilization of the world's sustainable resources, i.e., biomass. One way is to engineer microorganisms and animals with the capability of digesting and utilizing cellulosic materials, and plants which can be easily degraded by cellulolytic enzymes. In this article, we summarize recent studies on the molecular breeding of cellulolytic organisms for biomass utilization along with some considerations regarding cellulolytic enzymes.     

Purification and some properties of a chitinase from Xanthomonas sp. strain AK

Chitinase B (ChiB) was purified from the culture supernatant of Xanthomonas sp. strain AK by Phenyl-Toyopearl 650M and DEAE-Toyopearl 650M column chromatographies. The purified enzyme preparation gave a single band on SDS-polyacrylamide gel electrophoresis and the molecular weight of ChiB was estimated to be 48,000. The enzyme was optimally active at pH 6.0 and 60 degrees C. N-Terminal amino acid sequence analysis suggested that ChiB is a member of glycosyl hydrolase family 18 and that it is genetically different from ChiA recently reported (Sakka et al., J. Ferment. Bioeng., 86, 527-533, 1998). Immunological analysis suggested that ChiB was the major chitinase species in the culture supernatant of Xanthomonas sp. strain AK and that production of the enzyme was induced by the presence of chitin.     

Development of double sided linear pulse motor

Several novel design processes have been employed to develop two types of small linear pulse motors (LPM) with high thrust and high reliability. These LPMs are small enough for use in an implantable artificial heart. High thrust force is secured by means of a double-sided structure. A laminated core of cobalt steel plates and a rare earth magnet have been employed as the magnetic materials. One LPM has a two-phase, eight pole, four-coil construction and has been developed with the principal aim of miniaturization. The other has a two-phase, twelve-pole, two-coil construction and has been developed chiefly for ease of manufacture. Both types of LPM can have two to five times better input watt ratio, mass ratio, and volumetric ratio in relation to generated thrust than the conventional LPM     

Superiority of nitrate decomposition method for synthesis of K2NiF4-type LaxSr2−xMnO4 catalysts

K₂NiF₄-type La_0.2Sr_1.8MnO₄ was synthesized by nitrate (ND) and nitrate/acetate (NAD) decomposition methods as well as solid-state reaction. Single-phase oxide was obtained at 550 °C by the ND method just after the decomposition of Sr(NO₃)₂ and at 1000 °C by the NAD method after the decomposition of SrCO₃. The K₂NiF₄-type oxide was hardly formed by the solid-state reaction. In the La–Sr–Mn system, an intermediate compound of SrCO₃, if present or formed during the decomposition process, interfered with the low-temperature formation of the K₂NiF₄-type oxide because of its high decomposition temperature about 1000 °C. The ND method used only metal nitrates and no starting materials with carbon source, so that the low-temperature synthesis of the K₂NiF₄-type oxide was realized without forming obstinate intermediate compound of SrCO₃. The low-temperature synthesis was possible for La_xSr_2−xMnO₄ with the substitution of La (0 < x < 0.5) and not for La_0.2A_1.8MnO₄ (A = Ca and Ba). The effect of A-site cations on the K₂NiF₄-phase formation was discussed from the geometric aspect.