INHIBITORY EFFECT OF GLUCOSE ON TRYPTOPHANASE

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Abstract
The present studies attempted to elucidate the mechanism of the glucose inhibition of tryptophanase in Escherichia coli. The maximum level of tryptophanase activity was reached between 10 and 12 hours under both stationary and shaker conditions. However, the synthesis of the enzyme in the shaker-grown cells proceeded only after a lag of about 6 hours. The marked decrease in enzyme activity after 10 to 12 hours manifested by the shaker-grown cells was shown to be due to a dilution effect. The addition of glucose in appropriate concentration to the cultures at any time prior to the initiation of enzyme synthesis caused complete inhibition of tryptophanase formation; when added during the period of maximum enzyme synthesis (6 to 10 hours) further synthesis of the enzyme appeared to be halted. The concentration of glucose required for enzyme inhibition was about ten-fold greater in shaker-grown cells than in stationary-grown cells. Measurement of residual glucose in the medium revealed that shaker-grown cells utilized glucose more rapidly than stationary cells. A close correlation was found between residual glucose and tryptophanase activity. Tryptophan synthetase was inhibited by tryptophan and stimulated by glucose. Cells grown with tryptophan and glucose showed little synthetase activity. These data indicate that the inhibitory effect of glucose on tryptophanase is not due to the inhibition of a tryptophan per mease.

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