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The Journal of Cell Biology, Vol 55, 489-500, Copyright © 1972 by Rockefeller University Press

ARTICLE

BIREFRINGENCE OF SPERMATOZOA : I. Birefringence Melting of Squid, Bull, and Human Sperm Nucleoprotein



James Bearden Jr. 1 and Irwin J. Bendet 1

1 From the Department of Biophysics and Microbiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.

Dr. Bearden's present address is the Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77025.

In experiments designed to determine the thermal stability and bonding strength of a natural nucleoprotein structure, the loss of birefringence as a function of time and temperature was investigated for both mammalian and nonmammalian sperm nuclei. At a constant temperature, this reaction was found to be first order for both types over a range of temperatures. The methods of chemical kinetics applied to results of these reactions, called birefringence melting reactions, produced values for the enthalpy and entropy of activation in the reactions, which gave some indication of the strength of binding in the nucleoprotein structure; and these results, plus those on the influence of chemicals on the structure, were consistent with the molecular structures which have been proposed by others for the nucleoprotein complex of sperm nuclei. For both bull and human sperm in ethylene glycol, the rate-limiting step in the melting reactions appeared to be the breakage of disulfide bonds. For squid sperm in ethylene glycol, and bull or squid sperm in ethylene glycol plus ß-mercaptoethanol, the identity of this step was more ambiguous, but a possibility consistent with these and other results would be a cooperative breakage of ionic bonds.

Submitted on August 11, 1971
Revised on June 21, 1972


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