Regulation of glutaminase B in Escherichia coli. III. Control by nucleotides and divalent cations.

Glutaminase B from Escherichia coli is modulated by nucleotides and divalent cations. ATP and ADP inhibit glutaminase B whereas AMP and divalent cations activate it. Inhibition and activation required preincubation of the nucleotides with glutaminase B at 4 degrees. Mg2+, Mn2+, and Ca2+ activated the enzyme and prevented the inhibition by ATP. Dialysis in the presence of an activator ligand reversed the ATP inhibition of glutaminase B. The modulation of glutaminase B by energy charge is similar to that observed with other catabolic enzymes. We suggest that a pattern of reciprocal regulation of glutaminase B and glutamine synthetase by adenine nucleotides prevents the formation of a "futile cycle" of amide synthesis and degradation.