Crabtree effect
The Crabtree effect (after the English biochemist Herbert Grace Crabtree ; also "glucose effect") describes in the catabolism of baker's yeast ( Saccharomyces cerevisiae ) the effect that in the presence of higher glucose concentrations even in the presence of oxygen, i. H. under aerobic conditions, ethanol is formed.
This effect sets in when the glucose concentration exceeds a value of about 100 mg / l. The reason for this is that glucose represses the transcription of the respiratory genes. The pyruvate is not - as is usual under aerobic conditions - oxidized via the citric acid cycle and electron transport chain , but reduced to ethanol (fermented) . The Crabtree effect is of economic importance for the following reasons:
Baker's yeast is of great economic importance as a leavening agent for the production of baked goods. Under the anaerobic conditions of alcoholic fermentation , it converts various sugars (glucose, sucrose, fructose, maltose) into ethanol and carbon dioxide by means of glycolysis . This is normally different in the presence of oxygen: sugars are breathed into carbon dioxide and water, whereby the energy and thus the cell yield increase many times over.
If, however, ethanol is also formed under aerobic conditions under the conditions of the Crabtree effect, this leads to a dramatic reduction in the growth rate in the production of baker's yeast.
Individual evidence
- ^ Herbert Grace Crabtree: Observations on the carbohydrate metabolism of tumors . In: Biochemical Journal . tape 23 , no. 3 , 1929, pp. 536-545 , doi : 10.1042 / bj0230536 , PMID 16744238 .