Modeling of the velocity profile of a bioreactor: the concept of biochemical process

This research covers the modeling of the velocity profile of a bioreactor with recycle; the concept of biochemical process. The biochemical process adopted is fermentation and a plug-flow fermenter (PFF) was taken as a case study. The derivation of workable model equations for monitoring and predicting the velocity profile of a PFF were obtained, together with obtaining the model equations for investigating the effect of microbial and substrate concentrations on the discharge coefficient, bioreactor’s volume. Constant data were sourced from literatures, together with hypothetical values to simulate the derived model equations using Mathlab. The substrate concentration decreases with time as biomass population increases with time. Effect of biomass concentration on discharge coefficient, shows that increase in biomass concentration brings a corresponding increase in the discharge coefficient as well as the bioreactor’s volume revealed that substrate concentration is depleting alongside with bioreactor’s volume follows the same trend of change when substrate concentration is decreasing irrespective of whether the length or area of the bioreactor is varied. The effect of microbial concentration on bioreactor volume when area and length of bioreactor are varied reveals that the process followed same trend only that there is a presence of lag phase upon the influence of inhibitors. The inverse substrate concentration increases, the space velocity also increases, and there is a linear trend of change on the inverse substrate concentration with respect to space velocity.

In Vitro Selection of Cathepsin E-Activity-Enhancing Peptide Aptamers at Neutral pH

The aspartic protease cathepsin E has been shown to induce apoptosis in cancer cells under physiological conditions. Therefore, cathepsin E-activity-enhancing peptides functioning in the physiological pH range are valuable potential cancer therapeutic candidates. Here, we have used a general in vitro selection method (evolutionary rapid panning analysis system (eRAPANSY)), based on inverse substrate-function link (SF-link) selection to successfully identify cathepsin E-activity-enhancing peptide aptamers at neutral pH. A successive enrichment of peptide activators was attained in the course of selection. One such peptide activated cathepsin E up to 260%, had a high affinity (KD; ∼300 nM), and had physiological activity as demonstrated by its apoptosis-inducing reaction in cancerous cells. This method is expected to be widely applicable for the identification of protease-activity-enhancing peptide aptamers.

The Mechanism of Mus81-Mms4 Cleavage Site Selection Distinguishes It from the Homologous Endonuclease Rad1-Rad10

ABSTRACT Mus81-Mms4 and Rad1-Rad10 are homologous structure-specific endonucleases that cleave 3′ branches from distinct substrates and are required for replication fork stability and nucleotide excision repair, respectively, in the yeast Saccharomyces cerevisiae. We explored the basis of this biochemical and genetic specificity. The Mus81-Mms4 cleavage site, a nick 5 nucleotides (nt) 5′ of the flap, is determined not by the branch point, like Rad1-Rad10, but by the 5′ end of the DNA strand at the flap junction. As a result, the endonucleases show inverse substrate specificity; substrates lacking a 5′ end within 4 nt of the flap are cleaved poorly by Mus81-Mms4 but are cleaved well by Rad1-10. Genetically, we show that both mus81 and sgs1 mutants are sensitive to camptothecin-induced DNA damage. Further, mus81 sgs1 synthetic lethality requires homologous recombination, as does suppression of mutant phenotypes by RusA expression. These data are most easily explained by a model in which the in vivo substrate of Mus81-Mms4 and Sgs1-Top3 is a 3′ flap recombination intermediate downstream of replication fork collapse.

Incorporation of Excess Arsenic in GaAs and AlGaAs Epilayers Grown at Low Substrate Temperatures by Molecular Beam Epitaxy

ABSTRACTExcess arsenic can be incorporated in GaAs and AIGaAs epilayers by growing at low substrate temperatures (LT-GaAs and LT-AIGaAs) by molecular beam epitaxy (MBE). Upon annealing these epilayers, the excess As precipitates forming GaAs:As and AIGaAs:As. Using transmission electron microscopy (TEM), we have measured the densities and sizes of the As precipitates and thereby determined the amount of excess As incorporated in these epilayers. The volume fraction of excess As as a function of inverse substrate growth temperature follows an Arrhenius-type behavior with an activation energy of 0.87 eV. The sizes of the As precipitates increase and the densities decrease with increase anneal temperatures; for Si-doped GaAs:As this results in n-type material when the densities become small enough that the depletion regions around the As precipitates no longer overlap. Also investigated is the formation of As precipitates at GaAs/AIGaAs heterojunctions and superlattices, and our attempts to tailor the As precipitate distribution.