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Biomedical subjects

J Votruba

Publications and source records attributed to J Votruba.

34 records · Page 2Linked to original sources
PubMed1991

Effect of external pH on ethanol oxidation by Candida utilis.

The external pH affects both ethanol and oxygen uptake rates by nongrowing cells of Candida utilis suspended either in distilled water or in phthalate buffer. The buffering properties of organic acids control the maximum rates of exogenous respiration and ethanol uptake. The substrate limitation of ethanol uptake rate and endogenous respiration rate increase proportionally with increasing hydrogen ion concentration in the medium.

Candida↗
PubMed1991

Effect of external pH on acidification and excretion of ethanol intermediates by Candida utilis.

External pH affects the acidification induced by ethanol. The apparent specific rate of acidification depends on the dissociation properties and production of carbon dioxide, acetic and lactic acid which are intermediates of ethanol oxidation. The organic acids are transported by Nernst-Einstein diffusion. We designed and identified a new and simple mathematical model that allows us to describe the effect of external pH on nonstationary transport of dissociated intermediates of ethanol oxidation.

Acetates↗
PubMed1990

Population study of cell cycle in a continuous culture of Candida utilis.

The mean lengths of G1, S, G2 and M phases of the cell cycle were determined on the basis of the population distribution of Candida utilis grown in a continuous culture under steady-state conditions by using an original mathematical method. The length of the G2 phase was proportional to that of G1; the length of M was effectively independent of the growth rate. The length of S was proportional to the mean number of mitochondria in the cell.

Candida↗
PubMed1986

Fed-batch cultivation of Saccharomyces cerevisiae with increased content of delta 5,7-sterols.

Cultivation of Saccharomyces cerevisiae with a linear nutrient feed was used to test the validity of a mathematical model describing changes in the physiological state of the culture. Markers of these changes were the concentrations of proteins and delta 5,7-sterols in yeast dry mass. The model was used to optimize the production of these sterols with regard to the magnitude and composition of nutrient feed.

Computers↗
PubMed1986

Solenoid surface coils in magnetic resonance imaging.

A nonplanar solenoidal surface radiofrequency coil is used as a receiver with a conventional transmitter coil in a magnetic resonance imaging system. The improved signal-to-noise ratio, compared with that of conventional fixed saddle or solenoid receiver coils, permits higher resolution imaging and thinner image sections. In addition, the problem of signal dropoff that occurs in deep structures with planar and other noncircumferential surface coils is eliminated. Solenoid surface coils are particularly useful in imaging deep structures in anatomic regions that do not fit standard head and body coils, such as the neck, knees, and other smaller body parts.

Adult↗
PubMed1984

Kinetics of alpha-amylase production in a continuous culture of Bacillus licheniformis.

As found during continuous cultivation of Bacillus licheniformis on a semisynthetic medium (glucose or maltose as C source), the specific rate of alpha-amylase production is proportional to growth rate but is repressed by higher substrate concentrations. Besides glucose or maltose, peptone was also used as an alternative carbon source during cultivation. The specific rate of production of the enzyme on maltose is half that found with glucose.

Bacillus↗
PubMed1984

Kinetics of alpha-amylase production in a batch and a fed-batch culture of Bacillus subtilis.

Analysis of the kinetics of alpha-amylase production in a batch and a fed-batch culture of Bacillus subtilis made it possible to derive a kinetic model of the process describing mutual interactions between growth and production. The specific growth rate is limited by the concentration of both corn-steep liquor and starch. Higher concentrations of reducing sugars in the medium also inhibit growth. The overall production of alpha-amylase is a result of an equilibrium between the rate of enzyme production and its degradation due to the effect of environment. The actual specific production rate is directly proportional to the specific growth rate (characterizing the physiological state of the culture) and is inhibited by higher concentrations of corn-steep liquor in the medium.

Bacillus subtilis↗
PubMed1982

Stoicheiometry of dicyclohexylcarbodiimide-ATPase interaction in mitochondria.

1. The oligomeric dicyclohexylcarbodiimide (DCCD)-binding protein of mitochondrial ATPase was studied using (a) the relationship between (14C] DCCD binding and inhibition of ATPase activities and (b) the analysis of the kinetics of inhibition. 2. The [14C]DCCD binding to bovine heart mitochondria is linearly proportional to the inhibition of ATP hydrolysis up to a 50% decrease of the original activity resulting in 0.6 mol DCCD bound covalently to the specific inhibitory site (Houstĕk, J., Svoboda, P., Kopecký, J., Kuzela, S. and Drahota, Z. (1981) Biochim. Biophys. Acta 634, 331-339) per mol of the fully inhibited enzyme. 3. Kinetics of the inhibition of both the ATPase activity (heart and liver mitochondria) and ADP-stimulated respiration (liver) reveal that 1 mol DCCD per mol ATPase eliminates both the synthetic and the hydrolytic activities. It is inferred that the activity-binding correlation underestimates that number of DCCD-reactive sites. 4. The second-order rate constant of the DCCD-ATPase interaction (k) is inversely related to the concentration of membranes, indicating that DCCD reaches the inhibitory site by concentrating in the hydrophobic (phospholipid) environment. 5. At a given concentration of liver mitochondria, comparable k values are obtained both for the inhibition of ATP hydrolysis (k = 5.35.10(2)M-1.min-1) and ADP-stimulated respiration (k = 5.67.10(2)M-1.min-1). 6. It is concluded that both the synthetic and the hydrolytic functions if ATPase are inhibited via a common single DCCD-reactive site. This site is represented by one of the several polypeptide chains forming the oligomer of the DCCD-binding protein. The inhibitor-ATPase interaction does not exhibit cooperativity, indicating that the preferential reactivity towards DCCD is an inherent property of the inhibitory site.

Adenosine Triphosphatases↗
PubMed1982

Effect of aeration and mixing in various types of cultivation devices on the cell cycle of budding yeasts.

When investigating the effect of aeration capacity KLa of a cultivation device on the cell cycle of daughter cells of Candida utilis it was found that the length of a phase (S + G2) of the cell cycle is influenced by the rate of oxygen transfer. An increase of KLa of a cultivation device achieved by increasing the specific output of mechanical energy for air dispersion and mixing may lead to cell damage and to changes in the cell cycle. The effect of high intensity of aeration and mixing is thus invalidated.

Candida↗
PubMed1981

Control of the cell cycle of Candida utilis by external conditions.

A mathematical model of the cell cycle of Candida utilis in a continuous culture was formulated with respect to dilution rate. It makes it possible to express the duration of morphological stages in minutes, separately for mother cells and daughter cells. These values were compared with equivalent parameters in batch cultures. Duration of the morphological stage with buds was much longer in batch cultures as compared with the same value determined for a continuous culture according to the mathematical model. When using cultivation apparatus with a higher aeration capacity the (S + G2) phase, i.e. the stage bearing the bud, was reduced also in the batch cultures and approached the values determined for the continuous culture by means of the mathematical model.

Candida↗
PubMed1981

Mathematical analysis of the oncornavirus maturation process (virion RNA conversion and morphological condensation).

The rate of the maturation process of avian myeloblastosis virus experimentally estimated on the basis of genomic viral RNA conversion and morphological transition of virions was mathematically analysed. Three mathematical models were suggested and fitted to experimental data. It was found that: (a) model of simple kinetics (Model 1) does not agree with experimental data. Therefore, two hypotheses were considered in further mathematical modelling: (b) virions are identical in time of budding: maturation is dependent on the presence of a virion component which is degraded with time (Model 2). This model agrees with experimental data in all stages of the maturation process. (c) Virions are released from cells at different stages of assembly (Model 3). This model differs from experimental data especially in early stages of maturation. The hypothesis used for the construction of Model 2 seems to be the most plausible to explain the maturation process and is in agreement with data of murine leukemia virus maturation which was found to be accomplished by cleavage of p70 precursor protein.

Kinetics↗
PubMed1980

Determination of the optimal feeding regime during biosynthesis of erythromycin.

A systems approach to the analysis of the process of fermentaton of erythromycin in demonstrated. On the basis of biochemical and bioengineering data obtained in hydrodynamic tests and pilot plant fermentations of erythromycin a mathematical model for optimal technological parameters of growth of Streptomyces erythreus and product formation was postulated. The optimal regime was simulated and subsequently verified. The production of erythromycin increased to 112%.

Culture Media↗
PubMed1976

Application of mathematical optimization methods in microbiology.

Mathematical methods of experiment design have so far found little use in the optimization of microbiological processes. The conventional optimization procedure is still the transformation of functional relationship of n variables into n unidimensional optimizations; furthermore, the Box-Wilson gradient method is often used. This paper presents a review of methods used in other fields, and their application in microbiological practice. The methods are classified according to whether they require, besides the simple determination of the objective function (direct search methods), also the finding of its first (gradient methods) or second derivative (Newton-Raphson method). A modified Rosenbrock's method of direct optimum search and the gradient Box-Wilson method were used in parallel for the optimization of yeast growth on methanol. Their comparison showed that Rosenbrock's method is more suitbale for multiparameter systems.

Candida↗
PubMed1976

Bioengineering problems connected with the use of conventional and unconventional raw materials in fermentation. A review.

Some bioengineering problems connected with the use of conventional and unconventional raw materials in fermentation research and industry are reviewed. They include the effect of the physical state of different substrates (solid, liquid, gaseous) and considerations of physico-chemical processes, especially the identification of limiting steps. A new concept of classification of fermentors with respect to the macromixing properties is suggested and its applicability for different substrates is considered.

Bacteria↗
PubMed1975

Application of modified Rosenbrock's method for optimization of nutrient media used in microorganism culturing.

The Rosenbrock's procedure has been modified for optimization of nutrient medium composition and has been found to be less tedious than the Box-Wilson method, especially for larger numbers of optimized parameters. Its merits are particularly obvious with multiparameter optimization where the gradient method, so far the only one employed in microbiology from a variety of optimization methods (e.g., refs, 9 and 10), becomes impractical because of the excessive number of experiments required. The method suggested is also more stable during optimization than the gradient methods which are very sensitive to the selection of steps in the direction of the gradient and may thus easily shoot out of the optimized region. It is also anticipated that other direct search methods, particularly simplex design, may be easily adapted for optimization of medium composition. It is obvious that direct search methods may find an application in process improvement in antibiotic and related industries.

Culture Media↗