The study of the reaction of terminated oligomerization in the synthesis of oligo-(beta1-6)-glucosamines

The applicability of terminated oligomerization to the synthesis of oligo-(beta1-6)-glycosamines, fragments of the intercellular polysaccharide adhesin of staphylococci, was studied. The reactions of terminated oligomerization were carried out with mono-, di-, and trisaccharide monomers and N-protected aminopropanol; and spacered mono- and disaccharides as terminating molecules were also attempted. The primary formation of cyclic products of monomer intramolecular glycosylation was observed in almost all the reactions. Only the experiments with the monomer based on the disaccharide bromide under the conditions of the Helferich reaction led to reduced yields (30%) of the cyclic products. However, even in this case, the desired terminated oligosaccharides were generated in approximately 10% yield and mainly were the products of single glycosylation of the terminator by the monomer. These experiments allow the conclusion that, under the examined conditions, the reaction of terminated oligomerization could not result in the synthesis of oligoglucosamines with a high molecular mass.     

D-aspartic acid in the nervous system of Aplysia limacina: possible role in neurotransmission

In the marine mollusk Aplysia limacina, a substantial amount of endogenous D-aspartic acid (D-Asp) was found following its synthesis from L-aspartate by an aspartate racemase. Concentrations of D-Asp between 3.9 and 4.6 micromol/g tissue were found in the cerebral, abdominal, buccal, pleural, and pedal ganglia. In non nervous tissues, D-Asp occurred at a very low concentration compared to the nervous system. Immunohistochemical studies conducted on cultured Aplysia neurons using an anti-D-aspartate antibody demonstrated that D-Asp occurs in the soma, dendrites, and in synaptic varicosities. Synaptosomes and synaptic vesicles from cerebral ganglia were prepared and characterized by electron microscopy. HPLC analysis revealed high concentrations of D-Asp together with L-aspartate and L-glutamate in isolated synaptosomes In addition, D-Asp was released from synaptosomes by K+ depolarization or by ionomycin. D-Asp was one of the principal amino acids present in synaptic vesicles representing about the 25% of total amino acids present in these cellular organelles. Injection of D-Asp into live animals or addition to the incubation media of cultured neurons, caused an increase in cAMP content. Taken as a whole, these findings suggest a possible role of D-Asp in neurotransmission in the nervous system of Aplysia limacina.     

Caspase-dependent cleavage of 170-kDa P-glycoprotein during apoptosis of human T-lymphoblastoid CEM cells

Multidrug resistance (MDR) mediated by the drug efflux protein, 170-kDa P-glycoprotein (P-gp), is one mechanism that tumor cells use to escape cell death induced by chemotherapeutic drugs. Moreover, evidence suggests that cell lines expressing high levels of 170-kDa P-gp are less sensitive to caspase-mediated apoptosis induced by a wide range of death stimuli, including Fas ligand, tumor necrosis factor, and ultraviolet irradiation. However, the fate of 170-kDa P-gp during apoptosis is unknown. In this study, we demonstrate for the first time that 170-kDa P-gp is cleaved during apoptosis of VBL100 human T-lymphoblastoid CEM cells. Apoptotic cell death was induced by LY294002 (a pharmacological inhibitor of the phosphoinositide 3-kinase/Akt survival pathway), H2O2, and Z-LEHD-FMK (a caspase-9 inhibitor which has been recently reported to induce apoptosis in CEM cells). Using an antibody to a common epitope present in both the third and the sixth extracellular loop of P-gp, two cleavage products were detected, with an apparent molecular weight of 80 and 85 kDa. DEVD-FMK (a caspase-3 inhibitor), but not VEID-CHO (a caspase-6 inhibitor), blocked 170-kDa P-gp cleavage. Recombinant caspase-3 was able to cleave in vitro 170-kDa P-gp yielding two fragments of equal size to those generated in vivo. Considering the size of the cleaved fragments and their reactivity with antibodies, which recognize either the N-half or the C-half region of the protein, it is conceivable that the cleavage occurs intracytoplasmically. Since 170-kDa P-gp has been reported to counteract apoptosis, its cleavage may be a mechanism aimed at blocking an important cell survival component.     

Enantioselective Baeyer–Villiger Oxidation of Bicyclo[3.2.0]hept-2-en-6-One with Fungi: Optimization of Biotransformation and Use of TiO2 as Support of Cell Growth

Fungi from Amazonian forest soil (Ecuador) and an Italian factory were screened for Baeyer–Villiger (BV) oxidation of bicyclo [3.2.0]hept-2-en-6-one to 2-oxabicyclo[3.3.0]oct-6-en-3-one (Corey’s lactone). Isolates of Fusarium sp. and F. solani produced the (+)-(1R,5S)-lactone while isolates of Aspergillus terricola and A. amazonicus afforded the (−)-(1S,5R)-lactone. Highest conversions (85% yield and 70% enantiomeric excess) were obtained with A. amazonicus grown in presence of 2.7 mM titanium dioxide.     

Reactivity of Lipase in an Optically Transparent Lecithin-Gel Matrix

This paper describes a novel environment for enzymatic reactions, a phospholipid-type matrix simulating a biological lipidic structure, which allows direct measurement of reaction parameters by noninvasive spectroscopic means.     

Characteristics of Bioreactors Made with Urease and Nad Glycohydrolase Reversibly Bound to Immobilized Antibodies

The characteristics of urease and NAD glycohydrolase, immobilized on different matrices through linkage with polyclonal antibodies, were studied for their use as enzyme reactors. The stability of the derivatives was enhanced by immobilization but some leakage of activity was found, due to the equilibrium between the free and bound enzyme. The release of the enzyme to the solution depends on the affinity constant of the antibodies and the concentration of the substrate circulating in the reactor. On the other hand the main advantage of this easy method of immobilization is the low cost replacement of the inactive enzyme with fresh catalyst.