生物工程下游技术-第五章幻灯片.pptVIP

Separation and purification of products The mechanical methods are dominated by homogenization or ball mill grinding. In both cases, cells are broken by high mechanical shear. Heat generation is a problem. CHEMICAL METHODS The chemical methods of cell rupture are dominated by osmotic shock, detergent solubilization, and lipid dissolution. These three methods are described in the following paragraphs. Before this description, we want to give some brief generalizations about the other two methods: enzyme digestion and alkali treatment. Both enzyme digestion and alkali treatment are effective methods of cell rupture, but each has a major disadvantage. The disadvantage of enzyme digestion is the cost of the enzymes which Frequently makes this method prohibitive at a large scale. This is unfortunate, because the method is both gentle and selective. It is nothing more than adding to a cell suspension enzymes which react quickly with the cell walls and destroy them. Because the enzymes selectively catalyze these cell wall reactions, they react only sparingly with other solutes within the cell. Alkali treatment is the antithesis of enzyme digestion, for it is harsh rather than gentle, nonselective rather than specific, and cheap rather than expensive. Alkali added to a cell suspension reacts with the cell walls in a number of ways, including the saponification of lipids in the cell walls. In a sense, the treatment is an extreme example of solubilization, for it converts cell wall components into detergents. Including protein denaturations. As a result, the method tends both to rupture cell walls and to destroy products. Even though it is cheap, alkali treatment is less useful than the three methods which are detailed next. A、Osmotic Shock The simplest of the three major chemical methods is osmotic shock. This is nothing more than dumping a given volume of cells into pure water - often about twice the volume of cells. The cells swell because they contain solutes w