THE ACTIVATION OF STARFISH EGGS BY ACIDS

• Main Author: Lillie, Ralph S.
• Format: Text
• Language: English
• Published: The Rockefeller University Press 1926
• Subjects: Article; Carbonic acid
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2140768; http://www.ncbi.nlm.nih.gov/pubmed/19872205

1. Exposure of unfertilized starfish eggs to dilute solutions of weak acids (fatty acids, benzoic and carbonic acids) in isotonic balanced salt solution causes complete activation with the proper durations of exposure. For each acid the rate of activation (reciprocal of optimum duration) varies with concentration and temperature; at a given temperature and within a considerable range of concentrations (e.g. 0.00075 to 0.004 M for butyric acid), this rate is approximately proportional to concentration. We may thus speak of a molecular rate of action characteristic of each acid. 2. In general the molecular rate of action increases with the dissociation constant and surface activity of the acids. In the fatty acid series (up to caproic), formic acid has the most rapid effect, acting about four times as rapidly as acetic; for the other acids the order is: acetic = propionic ≦ butyric < valeric < caproic. Carbonic acid acts qualitatively like the fatty acids, but its molecular rate of action is only about one-fourteenth that of acetic acid. 3. Hydrochloric and lactic acids are relatively ineffective as activating agents, apparently because of difficulty of penetration. Lactic acid is decidedly the more effective. The action of both acids is only slightly modified by dissolving in pure (isotonic NaCl and CaCl2) instead of in balanced salt solution. 4. The rate of action of acetic acid, in concentrations of 0.002 M to 0.004 M is increased (by 10 to 20 per cent) by adding Na-acetate (0.002 to 0.016) to the solution. The degree of acceleration is closely proportional to the estimated increase in undissociated acetic acid molecules. Activation thus appears to be an effect of the undissociated acid molecules in the external solution and not of the ions. Acetate anions and H ions acting by themselves, in concentrations much higher than those of the solutions used, have no activating effect. The indications are that the undissociated molecules penetrate rapidly, the ions slowly. Having penetrated, the molecules ...