Regulation of Biodegradative Threonine Deaminase Synthesis in Escherichia coli by Cyclic Adenosine 3',5'-Monophosphate

Cyclic adenosine 3',5'-monophosphate (cyclic AMP) increases the rate of synthesis of biodegradative threonine deaminase in Escherichia coli made permeable by treatment with tris(hydroxymethyl)aminomethane and ethylenedia-minetetraacetate. Cyclic AMP overcomes the repression of the enzyme by glucose. In both cases, a half-maximal effect of the nucleotide occurs at about 1.4 x 10-4 m. Cyclic AMP does not influence the over-all rate of protein and RNA synthesis. Furthermore, it does not stimulate the conversion of inactive enzyme to an active form since it does not affect the enzyme level in cells in which protein synthesis is inhibited by chloramphenicol. The half-life of biodegradative threonine deaminase-specific messenger RNA is approximately 2 min and is also unaffected by the nucleotide. Cyclic AMP fails to stimulate enzyme production in cells in which messenger RNA synthesis is arrested by rifampicin or change of medium components. Thus, cyclic AMP appears to participate in the regulation of this enzyme synthesis at a transcriptional step. Among the nucleotide analogues tested, AMP and ADP stimulate the apparent rate of the enzyme production, but they do not counteract the repression of the enzyme by glucose. These compounds appear to stimulate the conversion of inactive labile enzyme to an active stable form, since they enhance the enzyme level in cells in which protein synthesis is inhibited by chloramphenicol.