Jose Ailton Conceicao Bispo

Substrate and enzyme concentration dependence of the Henri–Michaelis–Menten model probed by numerical simulation

The use of the classic Henry–Michaelis–Menten (HMM) model (or simply, Michaelis–Menten model) to study the substrate and enzyme concentration dependence of enzyme catalysis is a very important step in understanding many biochemical processes, including microbial growth. Although the HMM model has been extensively studied, the conditions in which the substrate concentration is not in excess have still not been adequately defined mathematically. This lack of definition occurs despite at the cellular and molecular levels most systems generally do not operate in a state of substrate excess. In the present work, we describe an approach for studying enzyme reactions in which substrate concentrations are not in excess. Our results show that the use of extent of reactions and numerical simulation of the velocities of reaction provides an important advance in this field and furnishes results not obtained in previous studies involving these aspects. This approach, in association with knowledge of the rate constants, provides a direct and easy means of examining the single substrate–enzyme profile during product formation at any enzyme–substrate ratio. This approach is more direct than previous models that required the use of empirical equations with arbitrary constants.

Strategies for Xylitol Purification and Crystallization: A Review

This paper reviews the literature on the main aspects of purification and crystallization of xylitol produced either by chemical or biotechnological routes. Different strategies have been used to clarify media containing xylitol: activated charcoal, pH adjustment, ion-exchange resins, membrane separation, chromatographic methods, liquid-liquid extraction, and precipitation, or a combination of these techniques. This study explores the most recent results of research work carried out in this field as well as the main approaches to recover and crystallize xylitol in a pure form. The effects of impurities, temperature, supersaturation, crystal seed amount, and size on xylitol crystal growth are also discussed.

Modeling Drying Isotherms Using a Structure Transition Model

Drying introduces structural changes in the target material that modify its interaction with water. In this work, we developed a model based on star fruit drying that considered two forms of interaction with water. This model provided a very good fit to the experimental data and was applicable to drying of other products such as apple, barley, and coffee. This model yielded better fits for data reported in the literature than other models. These findings suggest that the model is applicable to a wide range of systems.

Production and partial characterization of β-1,3-glucanase obtained from Rhodotorula oryzicola

ABSTRACT The current study aims to assess the kinetics of population growth of Rhodotorula oryzicola and the production of β-1,3-glucanase (EC 3.2.1.39) enzyme by this yeast. It also aims to obtain the optimum conditions of β-1,3-glucanase enzymatic activity by varying the pH as well as to study the enzyme thermostability. R. oryzicola population doubled within 12 hr. During this period, 9.26 generations were obtained, with 1 hr and 29 min of interval from one generation to the other, with specific growth rate (µ) of 0.15 (hr−1). The entire microorganism growth process was monitored during β-1,3-glucanases production, and the maximum value was obtained in the stationary phase in the 48-hr fermentation period. pH and temperature optimum values were 4.7 and 96°C, respectively. The enzyme maintained 88% of its activity when submitted to the temperature of 90°C for an incubation period of 1 hr. The results show that the enzyme can be used in industrial processes that require high temperatures and acidic pH.

Applying structural transition theory to describe enzyme kinetics in heterogeneous systems

Enzyme action was investigated by assuming the occurrence of different states of enzyme-substrate affinities. These states were considered to involve enzyme species with distinct abilities to form reaction product. The results obtained showed strong agreement with the experimental data for the action of peroxidase. This approach provides a powerful tool for predicting the kinetic behavior of other enzymatic processes in conditions not described before. An additional feature of this approach is the ability to characterize processes at any enzyme-substrate concentration ratio, including high enzyme-substrate ratios and enzyme inhibition by substrate or product. This proposal can also be used in systems with heterogeneity concerning the investigated enzyme.

Optimizing Drying Processes Using a Structural Transition Model and Entropy Change Maximization

We describe a new approach for drying optimization based on a structural transition model involving species with distinct degrees of hydration α, the ratio between the water content and the sample mass. The raw material used consisted of jackfruit (Artocarpus heterophyllus) seeds that were cooked and then dried at five temperatures (50, 60, 70, 80, and 110°C). The drying process could be described as the material possessing two predominant structures concerning the drying behavior. The resulting curves furnished thermodynamic parameters as Gibbs free energy, enthalpy and entropy of the drying process, which allowed optimization of the energy and time required for drying.