Cell-free extract

A cell-free extract is material obtained from disrupted biological cells after removing intact biological cells. Its biochemical activity can be tested separately from the whole organism. It can contain many enzymes and substrates, together with cofactor components; cell removal is different from purification of one component.

The cell-free extract experiment under yeast asks whether fermentation requires intact living biological cells. In his 1907 lecture, Eduard Buchner described grinding yeast with quartz sand and diatomite in a large mortar using a heavy pestle, wrapping the dough in canvas, then squeezing it in a hydraulic press. Adding concentrated sugar syrup to the expressed liquid produced carbon dioxide bubbles and foam; separate investigations identified ethanol.^[ref]

Activity persisted after filtration through cell-removing porcelain candles. Toluene inhibited live yeast fermentation while the cell-free extract retained activity, addressing a different objection from cell removal. These comparisons support extracted chemical machinery as the cause; bubbles alone would not identify alcoholic fermentation.^[ref]

The inference is activity outside intact living biological cells, not that biological cells are unnecessary for making or maintaining the machinery. Nor was this a purified single-enzyme mechanism: the lecture acknowledges unsuccessful purification and reports that two separated inactive fractions recovered fermentation when reunited. Such a reconstitution asks which components must work together, extending the initial separation of organism from chemical activity.^[ref]