Membranous tubes in pseudoscorpion spermiogenesis

The highly complicated differentiation of the spermatid in the pseudoscorpion Diplotemnus sp. is accomplished without the presence of microtubules. Instead membranous tubes measuring approximately 50 nm in diameter and closely associated with endoplasmic reticulum are found from early to mid spermatids. The lumen of the tube is devoid of electron dense contents but a fluffy material is attached to the cytoplasmic side. They run straight or slightly bent and are in open connection with the cell membrane. First appearing near the cell bridge of the interconnected spermatids they form a bundle in the longitudinal axis during a transitory phase of elongation. When the cell rounds off again the tubules together with the endoplasmic reticulum disappear. The arrangement of the tubes and their presence during abortive elongation of the spermatid suggest a supportive function commonly attributed to microtubules. Moreover, the open connection with the cell membrane and their close association with the endoplasmic reticulum may indicate their participation also in transport.     

Regulation of D-xylose utilization by hexoses in pentose-fermenting yeasts

The aldopentose D-xylose is one of the most abundant sugars in plant biomass and its efficient microbial utilization is of fundamental importance in the overall bioconversion of lignocellulosic materials into liquid fuels and chemicals. The discovery of pentose-fermenting yeasts in the early 1980's led to world wide interest because of the perceived potential for improved D-xylose fermentation to enhance the prospect of biomass conversions. However, the utilization of D-xylose by pentose-fermenting yeasts can be adversely affected by the hexoses, mainly D-glucose and D-mannose, which are usually present in high amounts in lignocellulosic hydrolysates. Research in the past several years has uncovered some of the regulatory effects of D-glucose on D-xylose utilization. However, much remains unknown about the mechanisms responsible for these effects. This review summarizes the current state of knowledge on the induction, repression and inactivation of D-xylose utilization in pentose-fermenting yeasts.     

Enzyme stability in downstream processing. Part 1: enzyme inactivation, stability and stabilization

In biotechnological recovery processes the instability of the product can lead to large losses in the sequence of recovery processes needed to purify the product. As the cost of the final active product is strongly dependent on the recovery yield, this will lead to an increase in product cost. Therefore knowledge of factors that influence stability is important. This Part 1 contains a review on the factors that influence stability. As stability is very important in enzyme purification this review deals about enzymes and their ability to retain catalytic activity. Inactivation mechanisms and agents are discussed. A short review is given of enzyme structure and stability. This is followed by stabilization strategies and methods.     

Growth Yields and Maintenance Coefficients of Unadapted and NaCl-Adapted Tobacco Cells Grown in Semicontinuous Culture

Comparison of carbon utilization between unadapted and NaCl (428 millimolar) adapted tobacco (Nicotiana tabacum L.) cells under substrate limited growth conditions was facilitated using semicontinuous culture. Growth yields (Y_g) and maintenance coefficients (m) of unadapted and NaCl adapted cells were similar, indicating that the efficiency of carbon utilization for growth was not altered as a result of salt adaptation and that no additional metabolic costs were associated with growth of adapted cells in the presence of a high concentration (428 millimolar) of NaCl. The Y_g (0.588 grams organic dry weight gain per gram sugar uptake) and m values (0.117 grams sugar uptake per gram organic dry weight per day) were comparable in spite of substantial physiological and biochemical differences that exist between unadapted and NaCl adapted cells. Apparently, a metabolic homeostasis governs biomass production of cells before and after adaptation to salinity.     

GTP-binding proteins in intracellular transport

One of the most exciting recent discoveries in the area of intracellular protein transport is the finding that many organelles involved in exocytic and endocytic membrane traffic have one or more Ras-like GTP-binding proteins on their cytoplasmic face that are specific for each membranous compartment. These proteins are attractive candidates for regulators of transport vesicle formation and the accurate delivery of transport vesicles to their correct targets.     

Design and mathematical description of differential contactors used in extractive fermentations

The performance of differential contactors for use in extractive fermentation is complicated by the effects of product formation in the contactor. When product formation is significant, approximate analytical solutions are presented for the performance of the contactor for two limiting cases: high and low substrate concentrations. When products are formed at a constant rate, there is a minimum raffinate solute concentration that can be obtained, in contrast to the behavior of a column in the absence of product formation. General equations describing the behavior of the system for product formation with backmixing in both phases are presented. The case of a stripping factor not equal to unity is considered.