Study by the Kerr effect of the action of enzymes on macromolecules

An electrical field applied across electrodes immersed in certain solutions renders the latter birefringent (Kerr effect). If the field is in the form of a rectangular pulse the rise and decay of the birefringence will lag behind that of the field. Measurement of the decay enables relaxation times to be determined. These depend on molecular size and shape. The action of an enzyme in breaking up molecules with consequent change in relaxation time may be conveniently followed by observing this effect. A brief description of the apparatus and underlying theory of the method is given and some results of a study of the action of deoxyribonuclease on calf thymus deoxyribonucleic acid in the presence of magnesium ions are presented. Two relaxation times were found. The number of magnesium ions present affected both the magnitude of the birefringence and the relaxation times but the enzyme affected only the latter. Increase in ionic strength caused a linear decrease of birefringence and a rapid decrease in relaxation times. No change in the relaxation times with time of enzyme action was seen initially but then a decrease was observed. The results reported agree qualitatively with results obtained by other workers using viscosity and light scattering observations.