Summary: The regulatory mechanism for glucoamylase synthesis in strain 4 was studied. Synthesis of the enzyme was induced in the presence of maltose and other carbohydrates containing maltose units. Smaller amounts of enzyme were produced in the presence of glucose or other monosaccharides like sorbose and xylose. Enzyme production was maximal with 0.5% starch as the carbohydrate source. At higher concentrations of starch, production of the enzyme was less. In glucose medium, both extracellular and intracellular glucoamylase activities were very low. When starch medium was supplemented with glucose, the extracellular enzyme activity decreased with increasing concentration of added glucose. Intracellular amylase was also detected. There was no appreciable change in the level of this enzyme activity in the presence of added glucose. Further, when glucose was added to the growing culture after 2 d in starch medium there was a marked decrease in glucoamylase synthesis, which was also proportional to the amount of glucose added. Enzyme synthesis was resumed as soon as the glucose concentration in the culture medium fell below a critical level. All these observations strongly suggest that in strain 4, extracellular glucoamylase synthesis is subject to catabolite repression.


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