Preparation and performance of immobilized yeast cells in columns containing no inert carrier

Schizosaccharomyces pombe was cultivated in a medium of glucose (10 g/L) malt extract (3 g/L), yeast extract (3 g/L), and bactopeptone (5 g/L) to form flocs. More than 95% of the cell population were flocculated. Variation in glucose concentration (from 10 to 100 g/L) did not affect flocculation. Yeast extract helped induce flocculation. Application of the immobilized yeast for the continuous production of ethanol was tested in a column reactor. Soft yeast flocs (50-200 mesh) underwent morphological changes to heavy particles (0.1-0.3 cm diameter) after continuously being fed with fresh substrates in the column. Productivity as high as 87 g EtOH L(-1) h(-1) was obtained when a 150 g/L glucose medium was fed. The performance of this yeast reactor was stable over a two-month period. The ethanol yield was 97% of the theoretical maximum based upon glucose consumed.     

Purification, characterization, and amino terminal sequence of xylose reductase from Candida shehatae.

D-Xylose is a major component of the carbohydrates derived from agricultural residues and forest products. Among more than two hundred known xylose-utilizing yeasts, only a few species are known to be able to ferment xylose anaerobically. Candida shehatae is one of such xylose-fermenting yeasts. Xylose reductase (E.C. 1.1.1.21) is a key enzyme responsible for xylose metabolism in xylose-utilizing as well as xylose-fermenting yeasts. In this paper, we report the development of a convenient and reliable procedure for the purification of xylose reductase from C. shehatae to near homogeneity. The amino acid composition and N-terminal sequence of the enzyme have also been analyzed. C. shehatae seems to contain only a single xylose reductase, but the enzyme has a dual coenzyme specificity for both NADPH and NADH. The enzyme is remarkably stable at room temperature and 4 degrees C.     

Effect of exogenous ascorbic acid intake on biosynthesis of ascorbic acid in mice

The effect of exogenous ascorbic acid intake on biosynthesis of ascorbic acid in mice has been studied. After the mice were on diets containing added ascorbic acid for two months, the activities of ascorbic acid synthesizing enzymes in the mouse liver homogenates were measured using L-gulono-gamma-lactone as a substrate. Exogenous ascorbic acid intake (0.5, 1 or 5% in the diet) was able to increase the concentration of ascorbic acid in the blood and to decrease the activities of ascorbic acid synthesizing enzymes in mouse liver. The results suggest that ascorbic acid synthesis was controlled by local regulatory mechanism or by the concentration of ascorbic acid in the hepatic portal blood. Ingestion of dietary erythorbic acid, a stereoisomer of ascorbic acid, had no effect on the activities of ascorbic acid synthesizing enzymes.     

The low temperature,rapid dissolution of gellan away from root cultures

Summary A buffer system consisting of 50 mM Tris-HCl-TRIZMA base plus 10 mM EDTA was used to rapidly dissolve gellan gels used for maintaining transformed carrot root cultures. The optimum conditions of pH 7.5 in the presence of 10 mM EDTA for dissolving gellan were first worked out on a model test system containing 0.4% gellan, 0.025% MgSO₄·7H₂O, and blue dye. The conditions were then tested on gellan gels (0.2% gellan plus nutrients) containing carrot roots. This gel dissolution system was rapid (18 to 20 min), did not require heating, and could also be efficiently performed at 4 °C. Furthermore, the buffer system used for gel dissolution is a standard one used for plant cell fractionation studies.     

Effects of wall shear stress and fluid recirculation on the localization of circulating monocytes in a three-dimensional flow model

There is a correlation between the location of early atherosclerotic lesions and the hemodynamic characteristics at those sites. Circulating monocytes are key cells in the pathogenesis of atherosclerotic plaques and localize at sites of atherogenesis. The hypothesis that the distribution of monocyte adhesion to the vascular wall is determined in part by hemodynamic factors was addressed by studying monocyte adhesion in an in vitro flow model in the absence of any biological activity in the model wall.

Suspensions of U937 cells were perfused (Re = 200) through an axisymmetric silicone flow model with a stenosis followed by a reverse step. The model provided spatially varying wall shear stress, flow separation and reattachment, and a three-dimensional flow pattern. The cell rolling velocity and adhesion rates were determined by analysis of videomicrographs. Wall shear stress was obtained by numerical solution of the equations of fluid motion. Cell adhesion patterns were also studied in the presence of chemotactic peptide gradients.

The cell rolling velocity varied linearly with wall shear stress. The adhesion rate tended to decrease with increasing local wall shear stress, but was also affected by the radial component of velocity and the dynamics of the recirculation region and flow reattachment. Adhesion was increased in the vicinity of chemotactic peptide sources downstream of the expansion site. Results with human monocytes were qualitatively similar to the U937 experiments.

Differences in the adhesion rates of U937 cells occurring solely as a function of the fluid dynamic properties of the flow field were clearly demonstrated in the absence of any biological activity in the model wall.     

Production of Ethanol from d-Xylose by Using d-Xylose Isomerase and Yeasts

d-Xylulose, an intermediate of d-xylose catabolism, was observed to be fermentable to ethanol and carbon dioxide in a yield of greater than 80% by yeasts (including industrial bakers' yeast) under fermentative conditions. This conversion appears to be carried out by many yeasts known for d-glucose fermentation. In some yeasts, xylitol, in addition to ethanol, was produced from d-xylulose. Fermenting yeasts are also able to produce ethanol from d-xylose when d-xylose isomerizing enzyme is present. The results indicate that ethanol could be produced from d-xylose in a yield of greater than 80% by a two-step process. First, d-xylose is converted to d-xylulose by xylose isomerase. d-Xylulose is then fermented to ethanol by yeasts.     

Enzymatic and Microbial Preparation of d-Xylulose from d-Xylose

A high-d-xylulose mixture (d-xylose-d-xylulose = 33:67) was prepared from the cold ethanol extract of preisomerized d-xylose solution (d-xylose-d-xylulose = 77:23). Fusarium oxysporum f. sp. lini and Aspergillus niger were demonstrated to preferentially utilize d-xylose in the mixture of d-xylose and d-xylulose. Chromatographically pure d-xylulose was thus obtained in 90% yield. A high-d-xylulose mixture was also incubated with Rhodotorula toruloides, Klebsiella pneumoniae, Candida utilis, or Mucor rouxii.d-Xylose and d-xylulose were simultaneously consumed. When borate was added to the mixture, a d-xylulose-borate complex was formed, and it could be used to protect d-xylulose from being utilized.     

Glycoproteins from human colonic adenocarcinoma. Isolation and characterization of cell surface carcinoembryonic antigen from a cultured tumor cell line.

Alterations in cell surface glycoproteins have been implicated in malignancy. We examined surface membrane proteins of a cultured cell line, SKCO-1, which had been derived from a human colonic adenocarcinoma. Cell surface labeling of SKCO-1 cells with galactose oxidase, followed by reduction with sodium borotritide, revealed five major labeled glycoproteins upon sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. At least three additional labeled glycoproteins could be detected if galactose oxidase treatment was preceded by neuraminidase treatment. Some, but not all, of the glycoproteins could be iodinated by lactoperoxidase. The predominantly labeled glycoprotein (GPI) had a molecular weight of 200,000 and co-migrated in SDS gel with carcinoembryonic antigen (CEA). GPI was not removed from the cell surface by EDTA, hypertonic saline, or sonication but was released from the membrane by detergents. This glycoprotein was subsequently purified using lectin-agarose columns and gel filtration. GPI was judged homogenous by protein- and carbohydrate-stained SDS-polyacrylamide gels and had an amino acid composition similar to that of CEA. The carbohydrate composition of GPI was qualitatively similar to CEA but quantitatively distinct. GPI had a greater proportion of sialic acid and galactosamine and less fucose and glucosamine than CEA. Immunological studies, however, demonstrated identity between GPI and CEA. A study of the turnover rate of GPI showed it to have a half-life of 5 days.