The recBC enzyme of Escherichia coli K12: premature cessation of catalytic activities in vitro and reactivation by potassium ions.

Abstract

It is shown that in vitro the degradation of native and single-stranded DNA as well as the hydrolysis of ATP by purified recBC enzyme ceases 2-3 min after the start of the reaction. The presence of potassium ions (60-100 mM), bovine serum albumin (1 mg/ml) or protein from cell-free Escherichia coli extract (10 microgram/ml) prevents the cessation of the activity. Once the cessation has occurred, the activity of the enzyme can be completely restored by the addition of potassium ions, but not by bovine serum albumin. Sedimentation studies revealed that, in contrast to the active recBC enzyme, the 'silent' enzyme is no longer associated with substrate DNA of high molecular weight. On the basis of these results and other observations it is hypothesized that during the degradation of DNA in the absence of potassium ions or bovine serum albumin the recBC enzyme is subject to an alteration of its molecular conformation which results in an inactive form.