Hydrolase and transferase activities of the beta-1,3-exoglucanase of Candida albicans.

The exo-beta-1,3-glucanase of Candida albicans (Exg) has a marked specificity for beta-1,3-glucosidic linkages as judged by the kinetic constants for p-nitophenyl beta-glucoside, beta-linked disaccharides of glucose (laminaribiose, gentiobiose, and cellobiose), oligosaccharides of the laminari series, laminarin and pustulan. The kcat/Km ratios for a series of laminari oligosaccharides from -biose to -heptaose showed that Exg has an extended substrate-binding site which contains at least five binding sites for sugar residues. Binding at position +2 (the third sugar residue) increases the kcat twofold while positions +3 and +4 lower the Km value further and thereby increase the catalytic efficiency. Exg catalyses an efficient transglucosylation reaction with high concentrations of laminari-oligosaccharides which specifically form beta-1,3 linkages and with yields up to 50%. The rate of the transglucosylation is concentration-dependent and can be more than 10 times faster than the hydrolytic reaction with excess donor substrates such as laminaritriose and laminarihexaose. The kinetics of Exg and the predicted substrate-binding site for up to five sugar residues are consistent with a recent structural analysis of the enzyme-binding site.     

<i>Trichoderma</i> spp. fostering growth on <i>Capsicum chinense</i> Jacq. seedlings and antagonistic against <i>Meloidogyne incognita</i>

Fourteen native strains of Trichoderma spp. from wildand agricultural pathosystems in the state of Yucatan, Mexico, with growth-promoting ability of Capsicum chinense Jacq. seedlings were evaluated and antagonistic effect of their filtrate against second-stage juveniles (J2) of Meloidogyne incognita. The strains Th05-02 and Th27-08 showed the best significant effects on plant hight variable increments 55.57 and 47.62%, theTh07-04 with 29.48% more root length, theTh02-01 and Th07-04 isolates increased from 48.71 to 84.61% in volume radical and 53.40% of total dry biomass. Statistical analysis (p≤0.001) of Th43 and Th43-13-14 filtrates caused 100% mortality at 24 and 48h. In the test of reversibility to 24 h after replacing the filtrates Th43-13, Th43-14, TH09-06 and TH20-07 by sterile distilled water, the J2 did not recover their viability, so they were considered as the best potential strains of Trichoderma spp. with antagonistic capacity in J2 of M.incognita.     

The reversible action of alpha-amanitin on nuclear structure and molecular composition

The effects of brief trypsin treatment on cell shape, surface topography, cytoskeletal components and the freeze-fracture distribution of plasma membrane intramembranous particles (PMP) are examined in contact-inhibited 3T3 cells. Untreated 3T3 cells are flat without many surface modifications, have highly organized microfilaments and microtubules and have clusters of PMP. Within seconds of trypsin treatment using a concentration of trypsin used for routine passage numerous zeiotic blebs appear on the cell surface which appear to “cap” or coalesce on the central superior aspect of the cell. In later stages retraction fibers are observed and the cells then round up and detach from the substrate. Using thin section transmission electron microscopy (TEM) the zeiotic blebs are observed and various constituents of the cytosol, including lysosomes, ribosomes, etc. pinch off and are surrounded by plasma membrane. In general there is a profound disruption of microfilaments and cortical microtubules. There is, however, a focal coalescence of microfilaments subjacent to the zones of the “capped” zeiotic blebs and some relative resistance of centriolar associated microtubules to tryptic degradation. Trypsin also causes profound changes in the nucleus which transforms from the normal round shape to a very convoluted and irregular shape. In addition to the zeiotic bleb formation which can be visualized by freeze-fracture the distribution of PMP goes from the normally clustered state to a more uniform distribution following treatment with trypsin. These studies suggest that there may be some coordinated control of the changes in cell surface topography, cytoskeletal components and intramembranous particle distribution.