726 6. O-IODOSOBENZOATE 



the toxicity (Luzzato and Satta, 1910). Probably the only useful role for 

 the carboxylate group is to increase the solubility. 



EFFECTS ON SEA URCHIN EGG DEVELOPMENT 



The effects of 0.66 mM o-iodosobenzoate in sea water on the development 

 of Arbacia eggs was studied by Runnstrom and Kriszat (1952). It was found 

 that fertilization and cleavage proceed quite normally up to the blastula 

 stage (perhaps with a slight delay), but after 6 hr the controls are hatched 

 whereas the treated ones are not. After 20 hr the controls are bilateral early 

 plutei, but 80-90% of the treated larvae are still within their membranes, 

 the formation of the entoderm being suppressed in these. The animal re- 

 gion is characterized by a high cylindrical region of epithelium carrying a 

 ciliary tuft, whereas the cells at the vegetal pole are flattened. The treated 

 larvae contain no pigment and the pigment initially present has disappear- 

 ed. This effect of animalization of the larvae can be brought about by other 

 enzyme inhibitors (iodoacetate, parapyruvate, etc.) and has been confirm- 

 ed for o-iodosobenzoate by Ranzi (1955). If the larvae after 6 hr exposure 

 to o-iodosobenzoate are removed to normal sea water, some recovery occurs 

 and fairly normal plutei may be formed, although the arms are lacking and 

 the archenteron shows no differentiation. The general conclusion was that 

 oxidation of certain SH groups suppresses primarily the differentiation of 

 the entomesoderm. 



A more detailed study of the earliest stages of Arbacia egg development 

 was made by Monroy and Runnstrom (1952). The high concentration of 

 2.64 mM o-iodosobenzoate does not prevent the fertilization reaction or the 

 formation of the fertilization membrane, but the membrane is somewhat 

 thicker and more refractile than normally. At 80 min the controls are in 2- 

 and 4-ceU stages with the membrane unchanged, whereas the treated eggs 

 are all in the 2-cell stage with conspicuous membranes. One hour later three 

 fourths of the treated eggs are cytolyzed with escape of pigment. The mem- 

 brane thickening and the escape of pigment seem to be correlated. If the 

 eggs are first centrifuged, thickening of the membrane occurs only at the 

 pole where the pigment is located. Thus the membrane changes do not ap- 

 pear to be due to a direct action of the o-iodosobenzoate. Possibly the na- 

 ture of the membrane and its later changes during development depend on 

 substances formed in the egg and metabolic inhibitors interfere in the pro- 

 duction or action of these substances. 



The exposure of Paracentrotus lividus eggs to 0.35-0.7 mM o-iodosoben- 

 zoate does not affect subsequent fertilization or suppress cleavage, although 

 hatching is prevented (Hagstrom, 1963), confirming the earlier results of 

 Runnstrom and Kriszat (1952) on Arbacia eggs. There are, nevertheless, 

 differences in the response. First, cleavage is somewhat accelerated: The 



