Evidence against the involvement of adenosine 3',5'-cyclic monophosphate in glucose inhibition of beta-galactosidase induction in Bacillus megaterium.

When Bacillus megaterium cells are grown on D-galactose as the sole carbon source, the cells actively synthesize beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23). However, D-galactose, when added to a glucose-grown culture, did not induce beta-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 significate rate, whereas further synthesis of beta-galactosidase was halted. Adenosine 3',5'-cyclic monophosphate (camp) or guanosine 3',5'-cyclic monophosphate (Cgmp) did not relieve the glucose inhibition of beta-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 beta-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.