Two yeasts, Candida arabinofermentans PYCC 5603T and Pichia guilliermondii PYCC 3012, which show rapid growth on l‐arabinose and very high rates of l‐arabinose uptake on screening, were selected for characterization of l‐arabinose transport and the first steps of intracellular l‐arabinose metabolism. The kinetics of l‐arabinose uptake revealed at least two transport systems with distinct substrate affinities, specificities, functional mechanisms and regulatory properties. The l‐arabinose catabolic pathway proposed for filamentous fungi also seems to operate in the yeasts studied. The kinetic parameters of the initial l‐arabinose‐metabolizing enzymes were determined. Reductases were found to be mostly NADPH‐dependent, whereas NAD was the preferred cofactor of dehydrogenases. The differences found between the two yeasts agree with the higher efficiency of l‐arabinose metabolism in C. arabinofermentans. This is the first full account of the initial steps of l‐arabinose catabolism in yeast including the biochemical characterization of a specific l‐arabinose transporter.

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The thermoresponsive behavior of the rhodamine B end-labeled double hydrophilic block copolymer (DHBC) poly(N,N-dimethylacrylamide)-b-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)) and the 1:1 segmental mixture of PDEA and rhodamine B end-labeled PDMA homopolymers was studied over the range of 10-40 degrees C at the air-water interface. The increase in collapse surface pressure (second plateau regime) of the DHBC with temperature confirms the thermoresponsiveness of PDEA at the interface. The sum of the pi-A isotherms of the two single homopolymers weighted by composition closely follows the pi-A isotherm of the DHBC, suggesting that the behavior of each block of the DHBC is not influenced by the presence of the other block. Langmuir-Blodgett monolayers of DHBC deposited on glass substrates were analyzed by laser scanning confocal fluorescence microscopy (LSCFM), showing schizophrenic behavior: at low temperature, the RhB-PDMA block dominates the inside of bright (core) microdomains, switching to the outside (shell) at temperatures above the lower critical solution temperature (LCST) of PDEA. This core-shell inversion triggered by the temperature increase was not detected in the homopolymer mixture. The present results suggest that both the covalent bond between the two blocks of the DHBC and the tendency of rhodamine B to aggregate play a role in the formation of the bright cores at low temperature whereas PDEA thermoaggregation is responsible for the formation of the dark cores above the LCST of PDEA.