Alteration of substrate affinities and specificities of the Chlorella Hexose/H+ symporters by mutations and construction of chimeras

The cDNAs HUP1 and HUP2 of Chlorella kessleri code for monosaccharide/H+ symporters that can be functionally expressed in Schizosaccharomyces pombe. By random mutagenesis three HUP1 mutants with an increased Km value for D-glucose were isolated. The 40-fold increase in Km of the first mutant is due to the amino acid exchange N436I in putative transmembrane helix XI. Two substitutions were found in a second (G97C/I303N) and third mutant (G120D/F292L), which show a 270-fold and 50-fold increase in Km for D-glucose, respectively. An investigation of the individual mutations revealed that the substitutions I303N and F292L (both in helix VII) cause the Km shifts seen in the corresponding double mutants. These mutations together with those previously found support the hypothesis that helices V, VII, and XI participate in the transmembrane sugar pathway. Whereas for most mutants obtained so far the Km change for D-glucose is paralleled by a corresponding change for other hexoses tested, the exchange D44E exclusively alters the Km for D-glucose. Moreover the pH profile of this mutant is shifted by more than 2 pH units to alkaline values, indicating that the activity of the transporter may require deprotonation of the corresponding carboxyl group. Chimeric transporters were constructed to study the 100-fold lower affinity for D-galactose of the HUP1 symporter as compared with that of the HUP2 protein. A crucial determinant for the differential D-galactose recognition was shown to be associated with the first external loop. The effect could be pinpointed to a single amino acid change: replacement of Asn-45 of HUP1 with isoleucine, the corresponding amino acid of HUP2, yields a transporter with a 20 times higher affinity for D-galactose. The reverse substitution (I47N) decreases the affinity of HUP2 for D-galactose 20-fold.     

Parallel architectures for AI semantic network processing

Artificial intelligence (AI) applications are growing in several fields, and in many such applications knowledge bases must be manipulated. This activity is usually performed by an external agent such as a central processor, but often this cannot supply the speed required. Knowledge-oriented architectures provide an efficient execution of knowledge manipulations. This paper provides an introduction to a particular subset of knowledge-oriented architectures, the semantic network approach, which is one of the most commonly used methods of representing and manipulating knowledge in the AI field. A brief overview of the semantic network components is presented in order to provide a background to the topic. The purpose of this paper is to review the proposed, implemented and/or simulated architectures for semantic network processing, and to discuss the capabilities and limitations of such architectures.     

On binary tree encodements⋆

Summary A data encoding scheme involving binary tree encodements is presented and analyzed. A closed-form formula for the number of n-bit legal memory configurations is developed. It is shown that the storage capacity loss due to the use of this scheme is not significant for large n.This work was supported in part under the NCHSR Grant HS03792 and the NIH Grant R R00396     

Performance analysis of zinc—bromine batteries in vehicle and utility applications

Rechargeable zinc—bromine batteries exhibit a number of inherent advantages that let them appear as possible candidates for applications in electric vehicles and utility load levelling. Based upon known single cell data, the performance characteristics of zinc—bromine batteries in vehicle and utility applications are predicted. The attainable specific energy and energy efficiency are computed as a function of specific power. The effects of specific cell resistance, self-discharge rate, and charge and discharge time on specific energy and efficiency are examined.     

Steps Toward Engineering Unity

The last century has witnessed the organization of professional societies in all fields of science and engineering. The consolidation of these societies into a unity such as the American Medical Association has been the aim of leaders in technology for many years. The following paper summarizes the actions taken and the plans proposed toward this much needed goal.     

Der Ungleichförmigkeitsgrad von dieselelektrischen Aggregaten bei Berücksichtigung der Wellenelastizität

Ohne Zusammenfassung Mitteilung aus dem lehrsluhl für Verfahrenslechnik der Technischen Hochschule München Schlu? des Aufsatzes aus Heft 5 (1956) S. 167/77.     

A floating sleeve antenna yields localized hepatic microwave ablation

We report a novel coaxial antenna for hepatic microwave ablation. This device uses a floating sleeve, that is, a metal conductor electrically isolated from the outer connector of the antenna coaxial body, to achieve a highly localized specific absorption rate pattern that is independent of insertion depth. This floating sleeve coaxial dipole antenna has low power reflection in the 2.4-GHz IMS band. Ex vivo experiments confirm our numerical simulation results. Index Terms-Ablation, coaxial aperture antennas, finite element methods, floating sleeve, microwave heating.