PubMed · 1608630
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R M Naclerio, A G Togias. 1992. Environmental influence: potential interactions.. https://doi.org/10.1177/019459989210600608
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Bacterial cellulose (BC) production was realized in a batch cultivation of Acetobacter xylinum subsp. sucrofermentans BPR2001 in a 50-L internal-loop airlift reactor. When the bacterium was cultivated with air supply, 3.8 g/L of BC was produced after 67 hours. When oxygen-enriched gas was supplied, the concentration of BC was doubled and the production rate of BC was 0.116 g/L. h, which was two times higher than that of air-supplied culture and comparable to that in a mechanically agitated stirred-tank fermentor. Bacterial cellulose produced by the airlift reactor formed a unique ellipse pellet (BC pellet), different from the fibrous form which was produced in an agitated stirred-tank fermentor. The BC-pellet suspension was demonstrated to have a higher volumetric oxygen transfer coefficient than the fibrous BC suspension in a 50-L internal-loop airlift reactor. The mixing time of BC-pellet suspension in the airlift reactor was also shorter than that in water.
Lignin peroxidase (LiP) has been used to study the C(alpha)-C(beta) cleavage of the propylene side chain in 1-(3',4'-dimethoxyphenyl)propene (DMPP) to 3,4-dimethoxybenzaldehyde (veratraldehyde, VAD). Under an air atmosphere, LiP oxidized DMPP to VAD (27.8%) and 1-(3',4'-dimethoxyphenyl)propan-2-one (DMPA, 8.7%), after 10 min of incubation. Dissolved O(2) was rapidly consumed during DMPP conversion, of which one-third was converted into superoxide. The remaining two-thirds of the consumed O(2) was involved in C(alpha)-C(beta) cleavage of DMPP to VAD and in self-propagating chemical reactions stimulating the consumption of DMPP. The involvement of peroxyl radicals, in the chemical consumption of DMPP, was confirmed by using the well-known peroxyl radical reductant Mn(2+). This metal ion severely inhibited the DMPP consumption rate under air, but did not affect the lower enzymic DMPP consumption rate under N(2). The substoichiometric requirement of LiP for H(2)O(2) during DMPP oxidation could be explained in part by dismutation of superoxide, but more importantly by direct chemical reactions of DMPP-derived peroxyl radicals with fresh DMPP. Another VAD-producing route was found by incubating the DMPP oxidation product, DMPA, with LiP. Under air the molar yield of VAD was 29.7%. In the absence of O(2), the C(alpha)-C(beta) cleavage of DMPA to VAD was strongly inhibited and side-chain coupling products (dimers) were formed instead. As a whole, the results suggest two new roles of O(2) in LiP-mediated oxidation of aromatic substrates. First, O(2) is responsible for the formation of reactive peroxyl intermediates, which can directly react with other substrate molecules and thereby accelerate consumption rates. Secondly, O(2) can prevent coupling reactions by lowering the pool of carbon-centred radicals accumulating during LiP catalysis.
The purified serotonin transporter (SERT) was spread at the air/water interface and the effects both of its surface density and of the temperature on its interfacial behavior were studied. The recorded isotherms evidenced the existence of a stable monolayer undergoing a lengthy rearrangement. SERT/ligand interactions appeared to be dependent on the nature of the studied molecules. Whereas an unrelated drug (chlorcyclizine) did not bind to the spread SERT, it interacted with its specific ligands. Compared to heterocyclic drugs, for which binding appeared to be concentration-dependent, a 'two-site' mechanism was evidenced for pinoline and imipramine.