Modeling biological gradient formation: combining partial differential equations and Petri nets

Both Petri nets and differential equations are important modeling tools for biological processes. In this paper we demonstrate how these two modeling techniques can be combined to describe biological gradient formation. Parameters derived from partial differential equation describing the process of gradient formation are incorporated in an abstract Petri net model. The quantitative aspects of the resulting model are validated through a case study of gradient formation in the fruit fly.

Disposal of waste liquor from 2,5-dichlorodisulfanilic acid production

Three alternative procedures were worked out for disposal of waste liquor from production of 2,5-dichlorodisultanilic acid [CAS No. 88-50-6]. This liquor is a hazardous liquid waste which, if discharged into a wastewater treatment plant without any treatment, inhibits processes of biological treatment. The first alternative utilizes stabilization/solidification technology by using fluidized-bed combustion ash. The second alternative consists in treating the liquor in a flow-through column packed with active carbon black as an adsorbent and discharging of the treated liquor, which already displays an acceptable chemical oxygen demand level after removal of organic pollutants by adsorption, into a wastewater treatment plant. The third alternative comprises of passing the waste liquor through the column with active carbon black and stabilization/solidification of the treated liquor by fluidized bed combustion ash. Efficiency of the liquor disposal in cases of stabilization/solidification was evaluated by determining dissolved organic carbon content, conductivity, pH, and ecotoxicity of test specimens' leachates. From results it follows that the proposed procedures represent efficient disposal of given liquid waste.

Evaluation of relative contributions of two enzymes supposed to metabolise hydrogen peroxide in Paracoccus denitrificans

A biosensor exploiting an electrochemically mediated enzyme-catalysed reaction was used to quantify relative contributions of cytoplasmic catalase and periplasmic cytochrome c peroxidase to the overall rate of hydrogen peroxide breakdown in cells of Paracoccus denitrificans. The effects of antimycin (an inhibitor of electron flow to cytochrome c peroxidase), the reaction rate versus substrate concentration profiles for the whole cells and subcellular fractions, and the time courses of oxygen concentration demonstrated a profound decrease in the capacity of cytochrome c peroxidase to reduce H2O2 under in vivo conditions. The reason is suggested to be a competition for available electrons between the enzyme and terminal oxidases metabolising oxygen produced by catalase.