Luiz B. Carvalho

CdTe quantum dots conjugated to concanavalin A as potential fluorescent molecular probes for saccharides detection in Candida albicans

Semiconductor colloidal quantum dots (QDs) have been applied in biological analysis due to their unique optical properties and their versatility to be conjugated to biomolecules, such as lectins and antibodies, acquiring specificity to label a variety of targets. Concanavalin A (Con A) lectin binds specifically to α-d-mannose and α-d-glucose regions of saccharides that are usually expressed on membranes of mammalian cells and on cell walls of microbials. Candida albicans is the most common fungal opportunistic pathogen present in humans. Therefore, in this work, this fungus was chosen as a model for understanding cells and biofilm-forming organisms. Here, we report an efficient bioconjugation process to bind CdTe (Cadmium Telluride) QDs to Con A, and applied the bioconjugates to label saccharide structures on the cellular surface of C. albicans suspensions and biofilms. By accomplishing hemagglutination experiments and circular dichroism, we observed that the Con A structure and biochemical properties were preserved after the bioconjugation. Fluorescence microscopy images of yeasts and hyphae cells, as well as biofilms, incubated with QDs-(Con A) showed a bright orange fluorescence profile, indicating that the cell walls were specifically labeled. Furthermore, flow cytometry measurements confirmed that over 93% of the yeast cells were successfully labeled by QD-(Con A) complex. In contrast, non-conjugated QDs or QDs-(inhibited Con A) do not label any kind of biological system tested, indicating that the bioconjugation was specific and efficient. The staining pattern of the cells and biofilms demonstrate that QDs were effectively bioconjugated to Con A with specific labeling of saccharide-rich structures on C. albicans. Consequently, this work opens new possibilities to monitor glucose and mannose molecules through fluorescence techniques, which can help to optimize phototherapy protocols for this kind of fungus.

Comparative Study of Amylases from the Midgut Gland of Three Species of Penaeid Shrimp

ABSTRACT Amylases from the midgut gland of wild Farfantepenaeus subtilis (Pérez-Farfante, 1967) and Litopenaeus schmitti (Burkenroad, 1936), and farmed Litopenaeus vannamei (Boone, 1931) were characterized through studies on the effect of inhibitor and metallic ions, optimal pH and temperature, thermal stability and zymograms. The substrate zymogram revealed nine, eight, ten and seven amylolytic bands from F. subtilis, L. schmitti, adults and juveniles L. vannamei, respectively. Total amylolytic activity in the farmed shrimp was three times as high as that of the wild specimens. Amylases from all species exhibited residual activity above 85% at alkaline pH (7.0–8.0), with optimal temperature between 40 and 50°C. None of the enzymes from the species were thermally stable at temperatures above 55°C. Alpha-amylase activity in F. subtilis and L. schmitti was totally inhibited by Type I inhibitor at 50 and 100 µg.mL-1, while enzymes from adult and juvenile L. vannamei retained 43.5 ± 1.98 and 22.5 ± 0.65% of their activity, respectively, at these same concentrations. Ca2+ increased amylase activity in all species only at a concentration of 1 mM, inhibiting activity at 5 and 10 mM. All other ions employed (Cd2+, Zn2+, Hg2+, Cu2+ and Al3+) strongly inhibited amylase activity, regardless of the concentration used.

High sucrolytic activity by invertase immobilized onto magnetic diatomaceous earth nanoparticles

Graphical abstract

PROTEASES FROM THE HARPACTICOID COPEPOD TISBE BIMINIENSIS: COMPARATIVE STUDY WITH ENZYMES FROM FARMED AQUATIC ANIMALS

Abstract The harpacticoid copepod Tisbe biminiensis has been tested as live prey in marine crustacean and fish larviculture. The aim of the present study was to characterize the proteinases in the crude extract of T. biminiensis. Trypsin activity was assayed in the crude extract prepared by the homogenization of specimens reared under controlled laboratory conditions and fed on diatoms and commercial fish food. The physical-chemical and kinectics parameters were determined using BApNA as substrate. Optimal pH and temperature were 9.0 and 55°C, respectively. This enzyme was thermostable until 50°C. Using BApNA as substrate, the Km was 0.59 mM and the proteolytic activity was strongly inhibited by specific trypsin inhibitors. However, the presence of other proteases was observed using substrate-SDS-PAGE. Eight caseinolytic bands were observed in the zymogram, four of them were not inhibited by classical mammalian trypsin inhibitors. Trypsin from T. biminiensis showed similar properties to those described for species used in commercial aquaculture. These results demonstrate that T. biminiensis may be a source of proteases, including trypsin-like enzymes.