Optimization by experimental design of polyacrylamide gel composition as support for enzyme immobilization by entrapment

We have developed a methodology based on experimental design, to optimize a polyacrylamide gel as the support for enzyme immobilization, taking advantage of all the properties which this type of gel has. Monomer and crosslinking agent proportions are responsible for both the porous structure and pore size of the gel. A correct selection of those variables and suitable synthesis conditions leads to an increase in the activity retained by the gel. The path of steepest ascent method was used to obtain the relative maximum activity. The maximum retained activity was chosen with a central composite design in terms of the gel composition. The retained activity in the network, loss activity in the wash water, and loss activity due to steric impediment or blockage was modeled in terms of the variables responsible for the gel structure. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 497-506, 1997.     

Chlorophenol degradation by Phanerochaete chrysosporium

Degradation of chlorophenols by P. chrysosporium in static cultures has been studied. The influences of mycelium acclimation, co-substrate concentration and nitrogen source on phenol degradation were analyzed. With non-acclimated mycelium the maximal concentrations degraded were 150 ppm of o-chorophenol and 100 ppm of the isomers m- and p-chlorophenol. The substituted ortho-position on the aromatic ring was the preferred attack position. Meta- and para-positions were less reactive and resulted in a slower degradation rate than the ortho position. Nevertheless, with acclimated mycelium, an increase in the ability to degrade chlorophenol and a higher reactivity in meta- and para-positions were observed (degraded chlorophenol increased by up to 70% for the o-isomer and 50% for the m- and p-isomers with respect to non-acclimated mycelium). A decrease in glucose concentration caused a decrease in chlorophenol degradation rate. Twelve days were needed for complete degradation of o-chlorophenol with 10 g/l of glucose and 22 days when glucose concentration was decreased to 2.5 g/l. The reduction of ammonium tartrate caused a greater lag time, but not a decrease in chlorophenol degradation rate. Replacement of ammonium tartrate by ammonium chloride caused a decrease in chlorophenol degradation rate.     

On the glycocalyx,the external coat of the plasma membrane,of some secretory cells

Summary The free surface of epithelial cells of secretory organs (human placenta, lactating mammary gland of the rat, choroid plexus of man and rat) and of the accessory organs of the genital tract of the male rat is characterized by a plasmalemmal differentiation named glycocalyx or surface mucous coat. This structure is built up by filamentous or globular substructures.Two main ultrastructural types of the glyeocalyx were observed: 1) The filamentous type such as in the rat epididymis, which resembles the cat intestinal glyeocalyx (Ito, 1965) and that one of human transitional epithelium (Monis and Zambrano, 1968), and 2) The globular type, as observed in the lumen of the lactating mammary gland of the rat.Sialic acid was demonstrated histochemically in the luminal glyeocalyx of all organs studied. In addition, the glyeocalyx of acinar cells of the lactating mammary gland contains sulfate and phosphate groups which were identified by histochemical technics, using enzymatic digestion procedures, suggesting the chemical heterogeneity of this glyeocalyx.Present investigations follow the working hypothesis that the complex carbohydrates of glycocalyces become part of the product of activity of secreting cells.We thank Mr. Luis Iwakawa, Miss Silvia Falcón, Miss Elsa M. Orgnero for technical help, Miss Graciela Aliaga for secretarial assistance. Photography by Mr. H. Magnani. Dr. Hugo F. Carrer cooperated in the initial stages of this investigation.The authors acknowledge the use of the electron microscope of the Department of Pathology, Córdoba University Medical School, for which they thank Prof. E. Mosquera and Dr. E. Hliba. Dr. Hliba photographed picture number 4.     

Seed set after pollination with in-vitro-matured,isolated pollen of Triticum aestivum

Summary Immature pollen of two varieties of Triticum aestivum, at the stage right after the first pollen mitosis, was isolated from individual anthers and cultured in microcultures of microliter droplets. In a specifically designed medium, some of the pollen grains developed to maturity. These were applied to excised stigmas on agar, where they produced pollen tubes. Application to flowers in vivo led to seed set. Pollen was matured in vitro from a variety that produced a different protein banding pattern on SDS-PAGE as compared to the variety that was pollinated. The protein banding in the produced seeds showed the hybrid pattern, demonstrating that the seeds were not produced by self-pollination in this in-breeding species but by pollination with the in-vitro-matured pollen.     

Respiratory system of vegetative and sporulating Bacillus cereus.

The composition and organization of the Bacillus cereus respiratory system were studied. The abolition of NADH-dependent respiration in vegetative and sporulating cell membranes by near-UV light (360 nm) indicated that electrons reduce oxygen only through a quinone-cytochrome pathway. Difference spectroscopy demonstrated the presence of cytochromes b555, c548, aa3, b562, and a2. This composition and studies with respiratory inhibitors suggested that cytochromes are organized in at least two branches, one being highly sensitive to cyanide.     

Effect of lactic acid on diacetyl and acetoin production byLactobacillus casei subsp.rhamnosus ATCC 7469

Lactic acid or its acidity apparently play an important role in the regulation of the biosynthesis of flavor compounds inLactobacillus casei subsp.rhamnosus ATCC 7469. In pyruvate-containing media,L. casei produces lactic acid, acetoin, and diacetyl. A specific pH-dependent system is necessary for both the use of pyruvate and the induction of acetoin and diacetyl production. In cell extracts ofL. casei, lactic acid inhibits the enzymatic activity of acetolactate decarboxylase (ALD) and acetolactate synthetase (ALS); this effect does not occur in whole cells under standard physiological conditions. Lactic acid prevents the use of pyruvate, and the induction of acetoin and diacetyl production. When pyruvate-containing media are used, the pH must be kept close to 6.0 in order to obtain the best production of acetoin and diacetyl.