Evidence against the involvement of adenosine 3′,5′-cyclic monophosphate in glucose inhibition of β-galactosidase induction in Bacillus megaterium
When Bacillus megaterium cells are grown on D-galactose as the sole carbon source, the cells actively synthesize β-galactosidase (β-D-galactoside galactohydroIase, EC 3.2.1.23). However, D-galactose, when added to a glucose-grown culture, did not induce β-galactosidase, apparently because of the glucose inhibition of the transport of galactose. On the other hand, when glucose was added to a galactose-grown culture, the transport of galactose continued at a reduced but significant rate, whereas further synthesis of β-galactosidase was halted. Adenosine 3′,5′-cyclic monophosphate (cAMP) or guanosine 3′,5′-cyclic monophosphate (cGMP) did not relieve the glucose inhibition of β-galactosidase synthesis in the preinduced culture. A method which gave a reproducible assay of c[32P]AMP in Escherichia coli did not detect cAMP or cGMP in a B. megaterium culture undergoing β-galactosidase induction, but revealed the extracellular accumulation of two unknown phosphorylated compounds. Cell-free extracts prepared from galactose-grown cells did not catalyze the degradation of cAMP or cGMP.