J. Biol. Chem., Vol. 261, Issue 26, 12128-12133, 09, 1986
Differences in the kinetic properties of BamHI endonuclease and methylase with linear DNA substrates
G Nardone, J George and JG Chirikjian
BamHI endonuclease and methylase were found to exhibit a kinetic preference
for linear pBR322 DNA substrates containing the recognition site in a
central location. The Km values for substrates having the recognition site
in a terminal location were approximately 3-fold greater than those with a
centrally located site. This phenomenon may be partially due to facilitated
transfer of the enzymes to the recognition site over nonspecific flanking
sequences. The exploitation of facilitated transfer by these enzymes has
been inferred from studies demonstrating kinetic preferences for longer DNA
substrates. The reaction rates of the endonuclease were 9-fold greater with
full-length pBR322 DNA than with a 74-base pair derivative. The methylase
exhibits a kinetic preference for longer substrates but only under
conditions of comparatively higher DNA concentrations. In addition, the
methylase has the property of increasing long chain preference with
increasing salt concentrations up to 120 mM. Increasing salt concentrations
decreased the endonuclease's preference for longer substrates. Nonspecific
inhibition studies revealed qualitative and quantitative differences
between the two enzymes under catalytic conditions. These studies suggest
that BamHI endonuclease and methylase interact with nonspecific DNA in
different ways.