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Biomedical subjects

A E Humphrey

Publications and source records attributed to A E Humphrey.

15 recordsLinked to original sources
PubMed1996

Kinetic Analyses of Desulfurization of Dibenzothiophene by Rhodococcus erythropolis in Continuous Cultures.

Rhodococcus erythropolis N1-36, a desulfurization strain, was grown in continuous culture at 10 different dilution rates with 50 (mu)M dibenzothiophene sulfone (DBTO(inf2)) as the growth-limiting nutrient. The steady-state biomass, concentrations of substrate (DBTO(inf2)) and product (monohydroxybiphenyl), saturation constant (0.39 (mu)M DBTO(inf2)), and cell yield coefficient (9 mg of biomass(middot)(mu)M(sup-1) DBTO(inf2)) were measured. Continuous cultures at five temperatures allowed calculation of activation energy (0.84 kcal(middot)mol(sup-1) [ca. 3.5 kJ(middot)mol(sup-1)]) near the optimal temperature (30(deg)C) for growth. A washout technique was used to calculate the maximum specific growth rate (0.235 h(sup-1)), a value equivalent to a minimum generation time of 2.95 h.

Journal Article↗
PubMed1978

Estimation of fermentation biomass concentration by measuring culture fluorescence.

The fluorescence of a fermentation culture was studied for its application as an estimator of biomass concentration. The measurement was obtained by irradiating the culture with ultraviolet light (366 nm) through a glass window and detecting fluorescent light at the window surface at 460 nm. It was estimated that over one-half of the fluorescent material was intercellular reduced nicotinamide adenine dinucleotide, with the remainder being reduced nicotinamide adenine dinucleotide phosphate and other unidentified intercellular and extracellular fluorophores. The culture fluorescence was found to be a function of biomass concentration, together with environmental factors, which presumably act at the cellular metabolic level to modify intercellular reduced nicotinamide adenine dinucleotide pools (e.g., dissolved oxygen tension, energy substrate concentration, and inhibitors). When these environmental conditions were controlled, a linear relationship was obtained between the log of the biomass concentration and the log of the fluorescence. Under these conditions, this relationship has considerable potential as a method to provide real-time biomass concentration estimates for process control and optimization since the fluorescence data is obtained on line. When environmental conditions are variable, the fluorescence data may be a sensitive index of overall culture activity because of its dependence on intercellular reduced nicotinamide adenine dinucleotide reserves and metabolic rates. This index may provide information about the period of maximum specific productivity for a specific microbial product.

Journal Article↗
PubMed1976

Pore diffusion model for a two-substrate enzymatic reaction: application to galactose oxidase immobilized on porous glass particles.

An analysis of the pore diffusion model involving a two-substrate enzymatic reaction is presented. The resulting equations have been applied to the case of galactose oxidase catalyzed oxidation of galactose when the enzyme is immobilized on porous glass particles. The physical constants of the system were obtained by theoretical predictions and the enzyme concentration in the porous medium was derived from the experimental results. The calculations were performed with the assumption that the kinetic parameters of the enzyme remain unchanged upon immobilization. The theoretically calculated effectiveness factors were compared with the experimental effectiveness factors determined from the batch kinetic experiments and were found to be in agreement. The results are presented as effectiveness factor plots graphed as functions of bulk galactose and oxygen concentrations. The model was extended in order to study the effect of external mass transfer coefficients and pore enzyme concentrations on the effectiveness factors.

Adsorption↗
PubMed1976

Galactose oxidase: applications of the covalently immobilized enzyme in a packed bed configuration.

Galactose oxidase (E.C. 1.1.3.9) was covalently immobilized to chemically modified porous silica particles by reaction of the native enzyme with pendant benzoyl azide groups on the carrier. The enzyme loading on the carrier was 100-150 units per milliliter. The immobilized enzyme was incorporated into a hardware assembly suitable for the determination of galactose or lactose concentrations in complex biological fluids. The prototype instrument as described is suitable for continuous, on-line monitoring or discrete sample analysis. Reaction conditions can be readily provided which maintain global first order kinetics within the reactor and strict linearity of the procedure over a wide range of sample concentrations. Auto-inactivation of the immobilized enzyme can be prevented by K3Fe(CN)6 and long-term reactor stability can be achieved by the periodic application of the reagent to the enzyme reactor in situ.

Alcohol Oxidoreductases↗
PubMed1975

Dynamic and steady state studies of phenol biodegradation in pure and mixed cultures.

The microbial degradation of phenol by pure and mixed cultures of Pseudomonas putida was studied in batch, phenol-stat, and continuous culture systems. In the continuous culture runs, both steady state and transient experiments were performed. From these experiments, a model for the kinetic behavior of the organisms was evolved and an analysis performed on the stability and dynamic behavior of pure and mixed cultures. The results indicate that it should be possible to achieve phenol removal from wastewaters down to levels of 1-2 ppm in a single state system. However, because of the effect of substrate inhibition on kinetic behavior of the microorganisms, long lasting transients can occur. The transient behavior of such systems cannot be solely determined from mumax or Ks parameters, but must include a consideration of the transient size and response characteristic of the organism.

Kinetics↗
PubMed1975

Economical factors in the assessment of various cellulosic substances as chemical and energy resources.

Economic factors in the assessment of various cellulosic substances as chemical and energy resources are many and complex. No substrate nor conversion process can be singled out as significantly advantageous. Agricultural wastes appear to have the best volume and availability characteristics. If glucose is to be the end product, then it will probably have to compete with corn syrup. If SCP is to be the end product, then productivities of 2-4 g/liter-hr must be achieved and the protein demand be such that the product can sell for at least $225/ton. If alcohol is to be the end product, then an intermediate product stream of glucose and other sugars must be obtained for 1-3cent/lb of fermentable sugars.

Agriculture↗
PubMed1967

Computer simulation of fermentation systems.

Results of batch fermentation of gluconic acid by Pseudomonas ovalis were graphically analyzed to obtain a kinetic model to represent the data. Since gluconic acid was produced by the hydrolysis of a lactone intermediate, the model was necessarily represented by a set of kinetic equations. A computer simulation technique involving the use of the MIDAS program was developed to solve the system of nonlinear equations and to check the appropriateness of the model. Since the maximal specific growth rate and the rate constant for the production of the lactone intermediate varied with time, function generators were used to simulate these system parameters. The merit of using the MIDAS program was considered in relation to analysis and model testing in microbiological processes of similar types.

Computers↗
PubMedDate not supplied

Monitoring cell concentration and activity by multiple excitation fluorometry.

Four key cellular metabolic fluorophores--tryptophan, pyridoxine, NAD(P)H, and riboflavin--were monitored on-line by a multiple excitation fluorometric system (MEFS) and a modified SLM 8000C scanning spectrofluorometer in three model yeast fermentation systems--bakers' yeast growing on glucose, Candida utilis growing on ethanol, and Saccharomyces cerevisiae RTY110/pRB58 growing on glucose. The measured fluorescence signals were compared with cell concentration, protein concentration, and cellular activity. The results indicate that the behavior and fluorescence intensity of various fluorophores differ in the various fermentation systems. Tryptophan fluorescence is the best signal for the monitoring of cell concentration in bakers' yeast and C. utilis fermentations. Pyridoxine fluoresce is the best signal for the monitoring of cell concentration in the S. cerevisiae RTY110/pRB58 fermentation. In bakers' yeast fermentations the pyridoxine fluorescence signal can be used to monitor cellular activity. The NAD(P)H fluorescence signal is a good indicator of cellular activity in the C. utilis fermentation. For this fermentation NAD(P)H fluorescence can be used to control ethanol feeding in a fed-batch process.

Candida↗
PubMedDate not supplied

Optimal design of the tubular microporous membrane aerator for shear-sensitive cell cultures.

In this paper, a theoretical analysis of oxygen transport across the tubular microporous membrane is described. This analysis has provided some insight into the optimal design of the membrane aerator. It was found in this study, at fixed inlet pressure, that the overall membrane oxygen transfer rate increases with increased tubing length only up to a certain length, i.e., the "critical length". When a large membrane surface area is required, the fiber should be divided into parallel segments to increase the overall oxygen transfer rate. A manifold or a gas distributor can then be used to distribute gas into segments of tubing. The length of each segment cannot exceed the critical length. In addition, shorter tube segments should give a higher oxygen transfer rate per unit tube length; however, this advantage is counterbalanced by the fact that gas distribution into huge numbers of parallel tubings may not be uniform.

Cells, Cultured↗