A cell-free system is an in vitro tool widely used to study biological reactions that happen within cells while reducing the complex interactions found in a whole cell. Subcellular fractions can be isolated by ultracentrifugation to provide molecular machinery that can be used in reactions in the absence of many of the other cellular components.
Cell-free biosystems can be prepared by mixing a number of purified enzymes and coenzymes. Cell-free biosystems are proposed as a new low-cost biomanufacturing platform compared to microbial fermentation used for thousands of years. Cell-free biosystems have several advantages suitable in industrial applications:
- In vitro biosystems can be easily controlled and accessed without membranes. Cell-free protein synthesis is becoming a new alternative choice for fast protein synthesis.
- Very high product yields are usually accomplished without the formation of by-products or the synthesis of cell mass. For example, nearly 12 H2 has been produced per glucose unit of polysaccharides and water, three times of the theoretical yield of the best anaerobic hydrogen-producing microorganisms.
- In vitro biosystems can implement some biological reactions that living microbes or chemical catalysts cannot implement before. For example, beta-1,4-glucosidic bond linked cellulose can be converted to alpha-1,4-glucosidic bond linked starch by a mixture of intracellular and extracellular enzymes in one pot.
- Enzymatic systems, without the barrier of cellular membrane, usually have faster reaction rates than microbial systems. For instance, enzymatic fuel cells usually have much higher power outputs than microbial fuel cells.
- Enzyme cocktails can tolerate toxic compounds better than microorganisms.
- Enzyme mixtures usually work under broad reaction conditions, such as high temperature, low pH, the presence of organic solvents or ionic liquids.
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