[On mechanism of nonlinear laser cleavage of DNA]

Dependences of nonlinear laser cleavage of DNA on a concentration of the free-radical scavenger, beta-mercaptoethanol, have been measured. The obtained data rule out the free-radical mechanism of the nonlinear laser cleavage and agree with the mechanism based on two-quantum excitation energy transfer from a dye to DNA. A high concentration of beta-mercaptoethanol has been found to cause DNA hyperchromicity.