Separation of the fertilization membrane in Urechis and sea urchin eggs as a phenomenon caused by breakage of hydrogen bonds : II. Action of carboxylic acids

Abstract

1. 1. Some aliphatic and aromatic carboxylic acids were investigated as to their potency in causing the separation of the fertilization membrane in eggs of the sea urchin, Hemicentrotus pulcherrimus, and the probable role of hydrogen bonds in connecting the vitelline and plasma membranes was discussed. 2. 2. The eggs were first exposed to acidified sea water for various lengths of time and then transferred to normal sea water in which the elevation of the fertilization membrane was observed. The time of the exposure required for the membrane elevation was taken as the measure of the activity of the acids. 3. 3. Eggs, exposed to lower pH than p K, required less time for the membrane elevation. Formic, acetic, propionic, n-butyric, iso-butyric, n-valeric and iso-valeric acids were effective at their respective p K values, and their effectiveness was generally related to the number of carbon atoms they keep. 4. 4. The order of effectiveness of halogenated acetic acid analogues was iodoacetic > bromoacetic > chloroacetic, when compared at their respective p K values; the order also represented that of their alkylating power. 5. 5. Among chloro-propionic acids, α-acid had the lowest p K and was most effective in causing the membrane elevation: β-acid stood next, and propionic acid last in the activity and acidity. 6. 6. Aliphatic hydroxy-acids were not effective, supposedly owing to the formation of intramolecular hydrogen bonds which are rather strong in force. 7. 7. Thioglycolic and thiolactic acids were effective at their respective p K values in spite of possibility of their making intramolecular hydrogen bonds. The bonds seem weaker in force and would be easily cut when more atractive foreign molecules come near. 8. 8. Benzoic acid and its homologues, phenylacetic and cinnamic, were effective at their respective p K values; phenylpropionic acid showed only a slight potency. 9. 9. With a few exceptions, stronger acids, in a homologous series, are more effective than weaker members. 10. 10. Number of carbon atoms and the potency in causing the membrane elevation are closely related in higher aliphatic acids; the non-polar groups of these acids seem to help their penetration into the cells. 11. 11. The results on the whole seem to agree with the supposition that the acids penetrate the membrane most easily in the non-ionized form, but will exhibit the membrane-elevating potency when ionized and endowed with activity to compete with hydrogen bonds between the vitelline and plasma membranes, and that the carboxylate anions should be the site of the activity though certain non-polar groups in these acids may also act as the membrane elevator.