A light in multidrug resistance: Photodynamic treatment of multidrug-resistant tumors

The major drawback of cancer chemotherapy is the development of multidrug-resistant (MDR) tumor cells, which are cross-resistant to a broad range of structurally and functionally unrelated agents, making it difficult to treat these tumors. In the last decade, a number of authors have studied the effects of photodynamic therapy (PDT), a combination of visible light with photosensitizing agents, on MDR cells. The results, although still inconclusive, have raised the possibility of treating MDR tumors by PDT. This review examines the growing literature concerning the responses of MDR cells to PDT, while stressing the need for the development of new photosensitizers that possess the necessary characteristics for the photodynamic treatment of this class of tumor.     

Random analysis of amino acid pairs sensitive to variants in human coagulation factor IX precursor

In this study, we used a random approach to determine which amino acid pairs in human coagulation factor IX precursor are more sensitive to its 99 variants. The results show that the randomly unpredictable amino acid pairs are more sensitive to variants.     

A method for estimating torque-vector directions of shoulder muscles using surface EMGs

In this study, a new method is proposed to estimate the torque-vector directions of each shoulder muscle. The method is based on a multiple regression model that reconstructs shoulder torque, which is calculated from the hand force and posture, from the surface EMG of many muscles recorded simultaneously. The torque-vector directions of eleven shoulder muscles of four subjects were obtained at up to 30 different arm postures with this method. The mean confidence interval (p < 0.05) of the estimated torque-vector direction of each subject was 7.7-10.6 degrees. The correlation coefficient between the measured shoulder torque and reconstructed shoulder torque was between 0.76-0.84. The results for majority of the muscles were in accordance with previous studies, and reasonable from the viewpoint of anatomy. The torque-vector directions of a muscle, which are estimated with this method, have more of a functional meaning than a pure anatomical or mechanical one. These indicate the direction of the shoulder torque accompanying the muscle activation for a normal shoulder action that involves the cooperative contraction of many muscles.     

The Evolution of the Ribonucleotide Reductases: Much Ado About Oxygen

Ribonucleotide reduction is the only known biological means for de novo production of deoxyribonucleotides, the building blocks of DNA. These are produced from ribonucleotides, the building blocks of RNA, and the direction of this reaction has been taken to support the idea that, in evolution, RNA preceded DNA as genetic material. However, an understanding of the evolutionary relationships among the three modern-day classes of ribonucleotide reductase and how the first reductase arose early in evolution is still far off. We propose that the diversification of this class of enzymes is inherently tied to microbial colonization of aerobic and anaerobic niches. The work is of broader interest, as it also sheds light on the process of adaptation to oxygenic environments consequent to the evolution of atmospheric oxygen.     

A feedforward model of suppressive and facilitatory habituation effects

 Simple exposure to repeatitive stimulation is known to induce short-term learning effects across a wide range of species. These effects can be both suppressive and facilitatory depending on stimulus conditions: repeatitive presentation of a weak stimulus decreases the strength of the response (habituation), whereas presentation of a tonic stimulus following a series of weak stimuli transiently increases the response strength (dishabituation). Although these phenomena have been comprehensively characterized at both behavioral and cellular levels, most existing models of nonassociative learning focus exclusively on the suppressive or facilitatory changes in response, and do not attempt to relate cellular events to behavior. I propose here a feedforward model of habituation effects that explains both suppressive and facilitatory changes in response relying on the interaction between excitatory and inhibitory processes that develop in parallel on two different timescales. The model's properties are used to explain the rate sensitivity property of habituation and recovery and stimulus dishabituation. Received: 1 June 2001 / Accepted in revised form: 4 December 2001     

Ethanol production from corn cob hydrolysates by <Emphasis Type="Italic">Escherichia coli</Emphasis> KO11

Corn cob hydrolysates, with xylose as the dominant sugar, were fermented to ethanol by recombinant Escherichia coli KO11. When inoculum was grown on LB medium containing glucose, fermentation of the hydrolysate was completed in 163 h and ethanol yield was 0.50 g ethanol/g sugar. When inoculum was grown on xylose, ethanol yield dropped, but fermentation was faster (113 h). Hydrolysate containing 72.0 g/l xylose and supplemented with 20.0 g/l rice bran was readily fermented, producing 36.0 g/l ethanol within 70 h. Maximum ethanol concentrations were not higher for fermentations using higher cellular concentration inocula. A simulation of an industrial process integrating pentose fermentation by E. coli and hexose fermentation by yeast was carried out. At the first step, E. coli fermented the hydrolysate containing 85.0 g/l xylose, producing 40.0 g/l ethanol in 94 h. Baker's yeast and sucrose (150.0 g/l) were then added to the spent fermentation broth. After 8 h of yeast fermentation, the ethanol concentration reached 104.0 g/l. This two-stage fermentation can render the bioconversion of lignocellulose to ethanol more attractive due to increased final alcohol concentration. Journal of Industrial Microbiology & Biotechnology (2002) 29, 124–128 doi:10.1038/sj.jim.7000287 Received 20 February 2002/ Accepted in revised form 04 June 2002