Abstract: | We have studied the dichroism of various samples of calf thymus DNA (of molecular weight from 3 × 105 to 7 × 106) in pulsed electric fields. The results may be summarized as follows: - 1 We find that calf thymus DNA behaves in electrical orientation as if it possessed a large permanent dipole moment. This apparent moment is sensitive to such effects as Mg++ binding which lower the net charge on DNA.
- 2 The limiting dichroism at infinite field corresponds to an angle of at least 80% between the transition moments at 265 nm and the helix axis, and could be consistant with a number of known forms of DNA. This result is independent of DNA molecular weight. There is evidence that the conformation may be different in 80% ethanol.
- 3 The dichroism relaxation curves contain a component with a relaxation time of about 8 μsec, which is nearly independent of molecular weight, and a longest component which behaves either according to the Broersma theory for low-molecular-weight samples, or the Zimm-Rouse theory at high molecular weights.
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