Industrial fermentation processes are increasingly popular, and are considered an important technological asset for reducing our dependence on chemicals and products produced from fossil fuels. However, despite their increasing popularity, fermentation processes have not yet reached the same maturity as traditional chemical processes, particularly when it comes to using engineering tools such as mathematical models and optimization techniques. This perspective starts with a brief overview of these engineering tools. However, the main focus is on a description of some of the most important engineering challenges: scaling up and scaling down fermentation processes, the influence of morphology on broth rheology and mass transfer, and establishing novel sensors to measure and control insightful process parameters. The greatest emphasis is on the challenges posed by filamentous fungi, because of their wide applications as cell factories and therefore their relevance in a White Biotechnology context. Computational fluid dynamics (CFD) is introduced as a promising tool that can be used to support the scaling up and scaling down of bioreactors, and for studying mixing and the potential occurrence of gradients in a tank.
Chimeric molecules consisting of parts from the sarcoplasmic reticulum Ca"-ATPase and the Na+,K'-ATPase were expressed in COS-1 cells and analysed functionally. One chimera, in which most of the central cytoplasmic loop was derived from the Na',K+-ATPase, while the transmembrane segments and the minor cytoplasmic loop came from the Ca*'-ATPase, was able to occlude Ca" and to be phosphorylated from ATP with normal apparent affinity for Ca*+ and ATP. This chimera also displayed normal sensitivity to thapsigargin, but was unable to undergo the transition from ADP-sensitive to ADP-insensitive phosphoenzyme and to transport Ca 2+ The other chimera, which consisted of the NH,-terminal two-thirds of .Na',K'-ATPase and the COOH-terminal one-third of Ca*'-ATPase, was unable to phosphorylate from ATP, but phosphotylated from inorganic phosphate in a Ca'+-inhibitable and thapsigargin-insensitive reaction. These results can be explained in terms of a structural model in which the non-conserved residues in the central cytoplasmic domain of the Ca2'-ATPase are without major importance for the binding and occlusion of Ca", but are involved in the ElP-+EZP conformational changes of the phosphoenzyme, whereas residues in transmembrane segments on both sides of the central cytoplasmic domain are involved in formation of the Ca"-binding sites. The data moreover show that thapsigargin sensitivity is dependent on residues in the NH,-terminal one-third of the Ca"-ATPase molecule.
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