The transglycosylation activity of a novel a-glucosidase from the basidiomycetous yeast Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) was studied using maltose as glucosyl donor. The enzyme synthesized oligosaccharides with a-(1 ! 2), a-(1 ! 4) and a-(1 ! 6) bonds. Using 200 g/l maltose, the yield of oligosaccharides was 53.8 g/l, with prebiotic oligosaccharides containing at least one a-(1 ! 6) linkage (panose, 6-O-a-glucosyl-maltotriose and 6-O-a-isomaltosyl-maltose) being the major products (47.1 g/l). The transglycosylatying yield was 3.6 times higher than the observed with the a-glucosidase from Saccharomyces cerevisiae (53.8 vs. 14.7 g/l). Moreover, when increasing the maltose concentration up to 525 g/l, the maximum production of tri-and tetrasaccharides reached 167.1 g/l, without altering the percentage of oligosaccharides in the mixture. Compared with other microbial a-glucosidases in which the main transglycosylation product is a disaccharide, the enzyme from X. dendrorhous yields a final product enriched in trisaccharides and tetrasaccharides. #

The adsorption of the antineoplastic drug mitomycin C (MC) on the hanging mercury drop electrode (HMDE) surface by means of stripping voltammetry measurements is studied. With this technique, a cathodic peak is obtained at −0.47 V (vs Ag/AgCl) in phosphate buffer pH 7.1 after accumulation onto HMDE surface by applying −0.35 V. Peak current variations with the accumulation time, MC concentration, and temperature are presented. The Langmuir isotherm is employed for adjusting the experimental results, and the values of the Gibbs free energy, enthalpy, and entropy of adsorption are calculated, the adsorption process being entropically governed. The results and data presented can provide useful information on the mechanism of penetration across the cellular membrane, which is of clinical interest since MC exerts its antineoplastic activity by interaction with biological membranes.

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Xanthophyllomyces dendrorhous grown in different media shows amylolytic activity, consisting in an extracellular exo-acting enzyme able to hydrolysed α,1-4 glycosidic bonds from soluble starch, which also cleaves maltose and malto-oligosaccharides. The enzyme was purified, using basically a couple of chromatography process on DEAE-Sephacel. It is a glycoprotein with a molecular weight estimated to be 60.2 kDa based on its mobility in SDS-PAGE and 115 kDa based on gel filtration. N-linked carbohydrate accounts for 12% of the total mass. It exhibited optimum activity at pH 5.5 and 45 • C. Thermostability analysis indicated that it was stable to thermal treatment up to 50 • C; 50% of the activity was maintained after 3 h. The rate parameters measured for the hydrolysis of starch and various chain length malto-oligosaccharides shows high catalytic efficiency, calculated by the relationship V cat /K m , for malto-oligosaccharides, such as maltotriose (873 mM −1 min −1 ), or maltoheptose (698 mM −1 min −1 ). The new enzyme hydrolysed soluble starch with nearly 3.5-and 1.4-fold lower efficiency than that for maltotriose and maltose, respectively. No activity was found on heterogeneous substrates, such as sucrose and aryl α-glucoside, or on isomalto-oligosaccharides. In accordance to substrate specificity profile, the new enzyme was classified as an α-glucosidase.